Molecules in the Spotlight

we had the public lectures committee we are very proud of the selected speakers

that we have and we have two types of speakers we have the distinguished

scientists that tell you about the leading edge research that they're doing here and we have the future

distinguished scientists who tell us about the leading edge research that are

just starting and this the latter case is what is happening today James crying

God his undergraduate degree from The Ohio State University and he came to

Stanford to work with Professor Philip buxbaum who is the director of the pulse

institute is the post Institute for a fast energy science and what I think is

going to happen tonight is that he and his colleagues who actually will be

known in the future as pioneers of ultra-fast x-ray science with lcls and

you're just witnessing science in the making gaze history in the making so you're privileged before I give the

floor to James there is one day to that I want you to write down which is March

23 why is that what is happening on March 23rd anyone has an idea yeah there

might be another lecture very good I just lost my job but the truth is we

don't have the title yet so the poor speaker is going to have only two months to prepare but it's going to be good as

usually is so check on our website and come back again so I talk too much let's

give the floor to James and let's welcome him with very warm

thank you is this can you can everybody hear me okay all right speak up okay so

thank you very much for that i'm here to present you a lecture entitled molecules

in the spotlight and it's all about an experiment we ran at the lcls so to start off i'll start where any good

lecture should with the speaker so this is me right here in the lab i'm an

atomic physicist card-carrying atomic physicist so what does that mean well that means I'm concerned about atoms and

also molecules molecules are just a couple of atoms bound together so what

can we do with atoms and molecules well when we can put them together to make everything well almost everything I'm

sure you guys can think of something see everybody in this room comprising is something that is included in everything

isn't made out of atoms and molecules but the vast majority of stuff is made out of atoms and molecules this includes

ducks both rubber and real and it includes planets both real and models

and it also includes cars so we could sit down and we could describe what

every atom and molecule inside a car is doing but there's actually an unimaginable number of atoms and

molecules inside a car so describing what every one of them is doing is not really the best plan and it will take a

lot of time and it will be very hard to do so that's why we invented engineers this is my little engineer

an engineers are very smart people who have lots of books and tables and have a lot of knowledge about how things work

together how large groups of atoms behave so cars not what we want to study by atoms and molecules so what would we

like to study it's part of everything well for instance we could study solar cells solar cells actually work on a

molecule by molecule basis we're interested with how light will interact with different atoms to convert into

electrical energy and where to even store energy this whole idea is called energy science and engineers work on

energy science too they use all of their their know how about how the physical world works and their books and their

tables right here depicted are here's our little engineer and they can study how solar cells work and they can try to

make them more efficient we approach it from another perspective right we're trying to rewrite the rules of how

things are working we're trying to look for new materials that might be important to make solar cells so not

we're not trying to build a better silicon we're trying to go a completely different direction so for instance we

could look at organic materials and here when I say organic I don't mean grown without chemicals like at the grocery

store you go and you buy organic fruit because it's not doesn't have preservatives no here organic means it's

made out of carbon the main thing is carbon and these organic materials are capable of converting optical or light

energy into electronic energy it happens all around us right for example plants every day create energy through a

process called photosynthesis which relies on this molecule right here chlorophyll so remember I showed you

that little dumbbell earlier and told you that this is a molecule and this is what I'm interested in well that little dumbbell is just like one little bar

here so if you look at this chlorophyll it's really complicated I mean it has

lot each of these little vertices right here is a carbon atom so this is made up of a bunch of carbon atoms plus some

other atoms and it's very complicated the structure itself is very complicated and so understanding site-by-site what

happens when light is shined on this molecule is very difficult and it's been

impossible to do so we have no idea right now where we have some basic ideas but no real

idea of what happens immediately after light shined on chlorophyll we just know that somehow electrical energy comes out

so how can we better study this well this is why we're all here the lcls so

I'm going to really quickly talk about what is the LCLs and why is it so special so here you can see the LCLs

right here here's to a tee most of you probably took this to get here possibly so you see the linear accelerator is

really long and we're right around in here this is a slack campus so what is the LCLs it's the world's first x-ray

free-electron laser which if you were here last two months ago probably you heard about this from the Daniel Ratner

and he told you all about how this amazing machine works so we'll talk about it really quickly it starts with

the already existing slack accelerator right here and it would that accelerates

a bunch of electrons now these electrons go through the accelerator and pass into right here where they are we have a

bunch of magnets we call these magnets unju laterz and what they do is they make these electrons wiggle when these

electrons wiggle they give off x-rays lots and lots of x-rays so that's one reason the LCLs is so special gives us

trillions and trillions of photons it's the McDonald's of photons and besides

this it's like McDonald's in another way to its really really fast so all of

these photons are delivered in about three and a half femtoseconds for our experiment at least which is an

incredibly short time so most of you might not be familiar with a femtosecond how short is it well we'll use a quick

analogy femtosecond is to a second as one second is to the age of the universe

so I'd say that's like a blink of an eye but it's so much shorter than a blink of an eye it's so hard to even think about

how how short this actually is so now we have this tool but how will we use this

to describe molecules well we'll do a molecular magic trick so you guys are

all probably familiar with the magic trick I'm about to describe you see the magician walk up to a table with a bunch

of place settings glasses and plates on it and then he really quickly pulls the

pulls the tablecloth out from under and leaves everything just sitting there so that's the trick but how is how are we

going to make the science well then we'll hold up the tablecloth and we'll look at the imprints of what was on the tablecloth

to see where everything was so this is a kind of trick that we're going to try to do with molecules and write like this

magic trick if you're ever trying to learn to do it which I tried to for this lecture and it didn't work so well that's why I use the graphing you don't

start with an entire place setting right you start with something simple so you'll put one glass or one plate on the

on the table and you'll try to pull the cloth out from under just one thing instead of a whole bunch so for ours we

tried nitrogen gas but there's other reasons we'll use nitrogen that we'll talk about in a minute but we just used

a simple nitrogen gas which is just two nitrogen atoms bound together so now to

further explain what I mean with this analogy to a magic trick we need to understand something about atomic structure so let's do a quick review you

guys probably have all seen this the periodic table maybe in chemistry class now I know you're thinking man we came

to a physics lecture what's he doing and talking about chemistry but it's all the same so what's important on the periodic

table well let's start with hydrogen the physicists best friend and as the

physicist best friend because it's so simple it's atomic number one so if you remember what an atomic number is great

if you don't all explain it in a second but it's atomic number one so it's the simplest atom that you can have so what

other what other atoms are important for us right now well we'll probably talk about carbon nitrogen and oxygen and

these are all very important in biology and inorganic materials so these are the main players that we're going to talk

about tonight okay so let's jump right into it let's talk about atomic structure so you guys all may remember

that atoms are actually made up of smaller pieces we made up of a nuclei and they're made up of electrons the

nuclei is actually made up of smaller pieces the proton in the neutron but for the purpose of this lecture we're just

going to talk about the nuclei is one part so as I said an atomic number the atomic number describes the number of

protons that are in the nucleus also we know that atoms are neutral things they

don't have a charge well protons are positively charged right we all probably remember that and electrons are nuclear

are negatively charged and remember opposite charges attract and like charges repel right do we all probably

remember that at some point we've learned that or played with magnets or seen something like this so we we know

that atoms are neutrally charged so if we have some number of protons we have to have the same number of electrons

okay so now we can start to talk about models of how an atom works and the

first model we're going to talk about is the planetary model developed by Ernest Rutherford after a series of experiments

in 1909 and here's our thrust referred right here and here's his model in his model the nucleus was the positive

charge sits at the center and the electrons orbit around that kind of like planets around the Sun which gives us

the name the planetary model however this model has problems electrons aren't

planets they have charges so weird things happen because they're charged so actually this model the atom is unstable

and these atoms would decay in less than a second so this is wrong so that this model doesn't work so what do you do

when your models broke you call a quantum mechanic

so this brings us to quantum mechanics which is the the theory that comes after after we talked about the planetary

model and here are some of the major players that were responsible for quantum mechanics there's many more but these four were exceptionally important

Heisenberg Schrodinger Einstein and Bohr all had very important roles to play in quantum mechanics the main idea behind

quantum mechanics is that electrons are like waves and as a result this means

that atoms are quantized now quantization this is a difficult concept so what do I mean when I say quantized

well let's think about it in terms of a hill so here we have just a normal hill with a ball on top of it the ball will

roll down the hill and the ball can sit can as its rolling down the hill can be at any height that it wants to be so we

call this a classical Hill now what if we quantize this Hill or made it quantum mechanical well now the ball can no

longer be anywhere it has to be at a certain height so it can either be at this height or this height or this height but it can't be anywhere between

so so far we see the quantum mechanics is a very black-and-white subject something is either black or it's white

there's no shades of gray here but the ball can still roll down the hill we see it just doesn't take it just only sits

at certain Heights so what does this mean when we compare it to atoms well now Adams from quantum mechanics we said

they were quantized what we mean is the energies of the electrons are actually quantized so they have discrete values

so the energy of an electron can either be here or here or here but it can't be anywhere between has to sit in one of

these levels the other important thing about these levels we learn from quantum mechanics is that like two bedroom apartments so two electrons can live in

each in each apartment and like any good apartment building they fill from the

bottom up because he wants to walk up the stairs if you don't eat it and so these electrons are just lazy so also

associated with each of these energy levels is in the is what we call an orbital which is very close to the word

orbit right that I used before but it's not an orbit right these things don't go around the nucleus they kind of sit

there and they're like waves and they sit there in a cloud so we call these clouds orbitals so what do these

orbitals look like well we can start with this very ground state or the very the lowest energy state

this has a name we call it the 1s and you can see a picture of it here you have the nucleus sitting at the center

and a cloud of electrons around it and this electron cloud looks like a sphere it's just a ball so now we move slightly

up in an edgy and we see okay now we just have a slightly bigger ball we still have this electron cloud and these

electrons can sit anywhere around here and we just have a bigger ball now we get a little weird we move to a slightly

higher energy and all of a sudden now we see something called a 2p now maybe you guys have seen this before a long time ago in a chemistry class or physics

somewhere but this 2p orbital right has two lobes so we have a see a lobe here

and elope here and they're colored two different colors just so you can tell just so you can differentiate there are two spots the electrons can be can be

you on the top or the bottom likewise we could orient this in any way so we could put a lobe here and a lobe here or a

load coming out at your and although behind the the page so we see there's actually three of these p three ways to

make these P levels so now we've talked a little bit about shape and these shapes are what would give shape to the

world around us and so now we know basically everything we need to know about atomic structure to move on so

what can we do with this what can we can we do now that we can describe atoms well we can just start to describe something more complicated molecules and

how do we make a molecule well like I said molecules are just atoms that are put together so we could take two atoms

and we can put them close to each other now when they're close to each other remember these electrons are in this

orbit or in these orbitals somewhere just bouncing around so what do they do well they feel each other's effects and

actually these clouds start to combine so they come together and they start to combine and you can combine them in two

ways and two very mathematical ways you could either add them and you would get a shape that looks like that or you

could bring your two atoms together and they're clouds could subtract and you get another shape like that again

through the red and the blue just mean that there are two places this could be so what can we say about these two

different shapes well remember I said the nuclei have protons in them that are positively charged and that like charges

repel each other so these nuclei don't want to be close together they want to pull the atoms apart and be set

rated but if we look at this cloud right here we see that we have some some

electrons in in between the through or we have some of the electron cloud in between the two nuclei now this effect

now you have positive charges with a negative charge in between and so these positive charges are actually pulled

towards this negative charge so a cloud like this actually pulls the nuclei together and binds the molecule and so

we call these orbitals these types of orbitals bonding orbitals now down here you see we have no electron cloud in

between right there's nothing in here so now the nuclei just see each other and they want to be pulled apart and these

these are types of orbitals tend to pull molecules apart so we call these antibonding orbitals see there we're

pretty good at naming so let's do an example let's talk about how we can use

what we know about bonding and antibonding orbital so here we have the physicist best friend hydrogen right

remember we said a hydrogen atomic number one has one proton so each hydrogen atom has one electron and it's

sitting here in this one s right because they feel from the bottom they feel like

a two-story apartment so now we can bring our two hydrogen atoms close together right remember we get a plus

and we get a minus so of our two shapes and now just like when we filled up the

atomic orbitals we can fill these molecular orbitals right here and we can do that and our two electrons hop in and

they're both sitting here in this binding orbital that wants to pull these these molecules together and they're

both really happy so they have little smiley faces they're happy being down there so this explains why all of the

hydrogen we see in our atmosphere is actually in the form of h2 and we don't see very much just normal hydrogen

floating around so now we can get slightly more complicated what's a little bit bigger than hydrogen well

helium helium is atomic number two it has two protons so it has two electrons we can see those guys sitting here we

can bring the two helium's together and we do the these combinations again and now we can go ahead and fill these

orbitals and now you see we have two of these electrons sitting down here in this bonding orbital that are happy and

we have two up here that are in these anti-bonding orbitals and they are very unhappy they don't want to be up here they want to pull

the nuclei apart so this explains why we don't actually see helium to you can't

go to the store and buy helium to it doesn't exist and this tells us why because now we we see that these two

electrons up here don't want to sit there so what can we do with all of this well now we can just start to describe

this experiment this that I was explained to you and we can also start to understand why some things bind

together and why some things don't bind together so I said in our experiment that we use nitrogen so we should

probably understand nitrogen before we move on so let's start to do that now nitrogen is a little bit more complicated so maybe we should start

with just the nitrogen atom first so remember we have these levels the one ask the 2s and the 2p and we remember

what those look like right the 1s a little ball the 2's a slightly bigger ball and the 2p has these weird lobes

right you're not too weird but it has these lobes so now what happens when we overlay all these on top of each other

just to get an idea of scale so we see that the 1s right here we can see it flashing right there we call this the

core and we see that these these orbitals or the electrons in this orbit are very close to the nuclei and are

very tightly bound and stay very close to the nuclei now if we look at the 2s it's flashing right there it's it's a

lot more spread out right it's not nearly as close to the nucleus and if we look at the 2p well we see that's way

far out there and remember this too p is a lot higher in energy so now we see that the 2p we call the the 2p the

valence that's just a name and we also call the 1s the core right right here we call this the core so the core is very

close to the nuclei and is very tightly bound the valence is very spread out not very tightly bound and has a large

spatial extent so actually these valence electrons are the electrons or these electrons in the valence are the

electrons that interact with the outside world and the core just kind of sits there it doesn't know anything about its environment has no idea what's going on

outside and the valances are the are the talkers right there they're the social

people so now we can go ahead and we can do the same idea we just did with hydrogen and helium and try to describe

how nitrogen bonds so now we see it looks a little bit more complicated right nitrogen has seven electrons so

there's there's a lot of them now we can bring our two nitrogen atoms to get and we get these energy levels right and

now we can start to fill our energy levels so first we'll start with the 1s they fill and you see we get a bonding

and anti-bonding so now we can fill the from this to s we're going to get another bonding and we get another

anti-bonding so so far we don't know if nitrogen wants to be bound or not so now we can do the peas and now look we have

three pairs of electrons in these bonding orbitals so they're very happy

so the nitrogen is the happiest thing we've seen so far so this explains these three electron pairs explain why

nitrogen atoms are very strongly bound in fact nitrogen is one of the strongest behind about one of the strongest bonds

you'll find in nature all right so we showed you what these orbitals look like when we are talking about atoms but do

they look the same for these molecules well let's see so we can start to look at these these orbitals so what are the

first the nuclei are these little black dots right we see those so what do the core orbitals look like right these are

the ones that are really close to the nucleus well that's these blue these little blue guy so you see these core orbitals are very distinct and separated

and are very close to the nucleus whereas the valence right remember that

term is this green blob that's spread out so the valence is spread out over the entire molecule where the core is

isolated around each nuclei in the molecule and the valence right we said

is the part that interacts with the outside world so what happens when molecules interact well that's what we

like to call chemistry so we just named it we said molecules interact and we call that chemistry and right we also

said that the interactions occur mainly through the valence are the electrons so

actually chemistry is the study of valence electrons that's all it is I mean if you're a chemist I'm sorry that

I dumped down your profession so much but really you're just studying the valence chemistry or the valence valence

electrons so how do you actually do that so now we know that they're there but how do we actually study them that's

pretty easy we just take a picture right it's very easy how do you how do you study something you take a picture of it

but can you actually just take a picture when you think of taking a picture right normally hold up a camera and you click the

button and something happens right but usually when you're taking a picture you're what's actually happening is you're opening some sort of shutter and

exposing some kite both film or sensor and then the shutter closes so what happens is the the action you're trying

to study is much faster then you can open and close the shutter which is definitely the case with atoms and

molecules but happens with other things in in life daily life around you two people sprinting is is faster than a

shutter can open and close well we developed something for that called a stroboscopic image so I know that's a

big word but strobe you can think of as like a strobe light we've all had we

probably all have seen a strobe light and watch them flash and walk in it and everything you can capture individual

things like they're standing still so this is a stroboscopic image of a cat jumping off a branch so what we do is we

we use short pulses of light or flashes of light to capture this so we leave an aperture open or we leave the exposure

open and we just flash a light real quick to capture the cat falling so what's important if we're taking

stroboscopic images well first thing is we need short light pulses or short flashes right if we have a really long

flash well then the motion of the cat just gets spread out and you don't really see anything if you use a really

short flash well now you start to resolve what the cat is actually doing and you can see how it falls and how it

twists what else is important well I mean this is a should've probably been

first but in order to study the motion the cat needs to jump off the branch right so just by having the camera there

the cat doesn't want to jump because maybe he's camera shy well that wouldn't be a good way to study it right or or

likewise if you want to get a picture of you and all of your friends and you take a picture and everybody blinks when the flash goes off well then you're not

going to get a very good picture this is the same idea with molecules right if we want to study molecules and the probe or

the light flash that we're trying to use bruins the molecule then it is in a very good way to study it right i mean i

think that would that sounds like pretty common sense so now remember what the whole idea we wanted to study right with

molecules was we wanted to study interactions of molecules on the level of what's going on at

individual site remember we showed chlorophyll and we at what's going on at each part that's what we want to study

so we want to know what's going on with each part of the cat in analogy right so

we can do that by studying the core of the cat and the core right if we cut study the core orbitals of a molecule we

see what each nuclei is doing because they're right around the nuclei whereas if we study the valence you can see everything gets kind of smeared out so I

don't know if you caught that will do it again so the core right you can see each a little part of the cat and how it's

twisting and turning and what it's doing to actually write itself and if we studied the valence of the cat which

isn't quite right we see that it's smeared out right and we can't really tell what's going on with each part of

the cat we can see that it's falling but we don't really know what's going on inside so how do we actually take these

pictures or we use light so what do we know about light you guys have maybe heard this before the light behaves like

a wave and a particle or a vertical and if dr. seuss were a physicist who

discovered this it would just be called al article but it wasn't dr. Seuss Einstein actually did a lot of work with

this and he died in the particle aspect of light which is what will focus on has

been called a photon and actually Einstein did work with this and he won the Nobel Prize for his famous equation

that e equals that's really close but it's actually hf but you guys almost had

it right so II here is the energy of a photon f is the frequency of the light

and H is a constant named after max plunk who actually was a hero of

Einstein so one of the few scientists that Einstein actually looked up to so

we probably all seen a picture of this before the electromagnetic spectrum probably when you come to these talks but we see right here we have so this

but normally we talk about this in terms of wavelength or frequency now we're going to talk about energy right because

energy and frequency from that equation are pretty similar right so we see visible light right here and we're all

familiar with visible light blue light up here has the highest frequency or is the highest energy photon and red light

is the lowest energy photon and lowest frequency so lower in energy than the visible

light are microwaves right which we're all probably familiar with we cook our food with them and these are how our

cell phones work or with microwaves now if we go slightly higher in energy we see the UV now the UV stands for

ultraviolet is very important it does it interacts with molecules quite well and

molecules like to absorb like to to react with UV light and if we go even higher in energy we see x-rays and this

is where the LCLs works is way down in the x-ray so way above the UV so we'll talk about that in a second right here

since I don't know I says it's censored right under the Patriot Act I don't know

what that's about so we should also mention that okay moving on so now we're

going to talk about how light interacts with matter right and we would say that a photon is absorbed if the energy of

that photon matches the difference between these atomic energy levels right so remember these energy levels right of

an atom are quantized right so it can only take a certain value it can't be in between so now here's an example of

absorption we have a hydrogen atom right it has a 1s energy and it has a 2p energy and now if a photon comes through

if it's at the right energy it can excite this electron likewise we can

talk about something called the photoelectric effect or you might know it as ionization or to better explain it

free electrons or created if the election if the energy of the photon is

greater than the energy that binds the electron to the material so the

photoelectric effect was actually first coined by Einstein in 1905 which contrary to popular belief he actually

won the nobel prize for the photoelectric effect and not for relativity he accurate relativity was

too controversial at the time to for him to win the Nobel Prize so they gave him the Nobel Prize for photoelectric effect

because he just did too many amazing things they just gave it to him for one of them so in here we have photons that hit a

material and then they excite these electrons and free them so really quick before we move on I'd like to remind you

real quick about nitrogen remember we have nitrogen atoms that come together to make these molecular orbitals or

molecular energy levels and then we fill it with electrons so we should remember what this structure looks like in here

because we're going to need that so here you see these again these are the nitrogen energy levels now what does

this look like what are these energies these of these things look like compared to these photons well so here's visible

light and visible light is about to EV now what's an EV EV is a measure of energy that's very convenient to use

when you're talking about photons so this is just a measure of energy so we see a visible photon is is very low

energy it doesn't have enough energy actually to to remove an electron from nitrogen now to remove a core electron

down here is the core remember it takes about four hundred EV that's a lot that's that's a lot more than a visible

than visible light this is in the x-ray area and the x-rays at the LCLs are

around a thousand EV so they're huge they're they're really high energy right

so now we can imagine doing an experiment right where we would we would

slowly turn up the photon energy and see what comes out right and watch the

electrons that come out so we're going to do that so right we see here here are occupied orbitals of nitrogen and now we

start with a very low photon energy right and now this doesn't have enough energy to make an electron so we don't

see anything now we turn up the energy a little bit more and all of a sudden we have enough energy to free and electron

and so over here we're going to we're going to plot our photon energy as we go this way and the number of electrons

that we see created so here we see a little peek now we increase the energy a little bit more and now oh we see

another peek right because now we can free this other level now we increase the energy just a little bit more and we

see we can free from this level and now we see three peaks here now if we increase a little energy a little bit more we don't

quite have enough met energy right so now we still see the same three peaks but we don't see anything else if we increase the energy a little bit more we

can free that level and create a free electron so we see another peak and if we keep going eventually we'll get to

the core and when we get to the core we'll see we can create a lot of electrons out of here so and remember

that the core was around x-ray wavelengths whereas all of these upper levels these valence levels were UV

energies right so the UV has an energy between 10 and 100 eV and these x-rays were a lot bigger than a lot higher

energy they were around 400 so what happens when we shine x-rays on our nitrogen Wow let's see when we've put it

when we shine an x-ray photon on our nitrogen we see that we'll just take one

of these core orbitals and will free it or this is shown schematically over here is a little hole right so we call these

these missing electrons in this core a core hole right and this state is

actually very unstable so let's think about a Jenga tower and if you take out

some of the pieces off of the bottom it's not very likely to stand up right if you just take a couple of pieces out

of the bottom that thing will fall over very quickly or at least when I play Jenga it falls over really quickly the

same is true here and actually these these these I guess configurations of

electrons will also decay very quickly and they decay through a process known as oj decay and an oj DK you can think

of two electrons are just bouncing around in these clouds and eventually they run into each other when they run

into each other one of these falls into this hole this core hole created right here and another one takes the extra

energy and is shot out and is freed from the from the atom or the neutral or the

molecule so we can see that schematically and that happens and this decay is very fast it happens in about

seven fifty seconds right so remember we said a femtosecond so this is like seven

seconds to the age of the universe if we were comparing it so a little background actually first on

Oh J to K 0 jada k was discovered by was the credit for OJT k was given to this

guy here PR oj he's a french physicist who a French atomic physicist who worked

with studying cosmic rays when he first observed this decay but actually three

years before an Austrian physicist Lisa Meitner actually first discovered a jdk

now it's tragic that she was overlooked in the naming what's even more tragic is after this she went on to discover

nuclear fission which is what runs all of our nuclear power plants and she said this with her colleague Otto Hahn and

then the Nobel Committee was looking at who to give the Nobel Prize for 24

nuclear fission and she was overlooked and the award was giving to Otto Hahn so

that's that's just tragic and I feel bad so for the rest of the lecture I'm going to retry to refer to it as oj might nerd

ok so now remember we had this ionization spectrum or this this graph

of energies of electrons when we turned up this photon energy wiki it the same

type of thing when we talk about these oj Meitner electrons right so we can

have this decay happen and then we can collect these electrons and we'll get a spectrum so this is our spectrum this is

going this way is the number of electrons we see and this way is energy so now you see there's a bunch of little bumps in here why are there bumps well

these bombs could happen because right we said this decay happens because two electrons run into each other well any

two electrons in here to run into each other so for instance this peak right here in red this happened because these

two electrons up here ran into each other and one filled the hole and the other left but over here this this peak

right here actually happened because this electron and this is electron ran into each other so you see each one of

these bumps happens because different pairs of electrons actually ran into each other and it's not just as easy as

I made it sound initially it's a little bit more complicated so now we'll do a quick reminder on the LCLs right we all

remember this it's the mcdonalds of x-ray photons right it makes trillions and trillions of them

and it's also really fast remember we said these pulses we use were about three and a half femtoseconds now that's

actually shorter than the oj time I told you a minute ago right i told you that these things don't decay for about seven

femtoseconds so this is much shorter so then what happens when the LCLs interacts with a nitrogen molecule well

first it's x-rays right so it's going to ionize from the core so the first x-ray photon comes in and ionizes one from the

core now before anything else can happen another photon comes by and ionizes another electron from the core and this

happens before so we see we have two core holes now one on each atomic 11

around each nuclei this happens before the valence electrons even have a chance to react so now these valence electrons

or are frozen in place and this core hole happens so that's interesting and

then also these core holes are even less stable so think about your ginga tower and now take away even more parts now

it's even more likely to fall over and it falls over in about two fifty seconds so what can we say about all these

things that we've just learned about let's summarize all of these things we know about double core holes so there we see the decay happen and we know right

we said the valence electrons are frozen in place when this decay happens and this decay happens very quickly and it

gives high energy electrons the other thing these double cores this energy of these electrons that come off are very

sensitive the separation and bonding between the two atoms so now we have a tool that we can use to study how these

atoms are linked together right so we've just built our molecular magic trick right and so to summarize to complete

the analogy our place setting here is the valence environment or the nuclear separation in these and these molecules

and our place mat is these double chord holes that I've been talking to you about and finally looking at the dimples

in the mat is like collecting the oj electrons so by doing all this we can do our molecular magic trick and I can lose

my license as a molecular magician because I just explained it to you so what you should know is that using this

technique we can measure the strength of a bond without disrupting the bond and we can we should be able to watch what

happens watch the readjustment of molecules as it happens as the nuclei move around we

should be able to watch them using this trick so this is all great and these

double core holes are an awesome tool but can you actually make them everything I've told you right now I've

just told you right I haven't shown you anything that says these happen well this is why we did in our experiment our

experiment the goal was to detect these double core holes and also to study their angular dependence so in order to

do that what do we have well we had this big contraption where we have a bunch of electron detectors and we shot the LCLs

in this way the LCLs came in with its photons this way or if we blow it up we can see it here we had the little

molecules the x-rays coming at them into the going into the the display and then

the electrons will first ionize an electron and then we'll have an oj electron come off so we'll have the

decay and so will will collect all of these electrons with these detectors right here this will collect the ions

that are left over and here is where we'll put our nitrogen into our experiment so this is just a rendering

right some an engineer drew this and just rendered it so it's really nice to see so what did it actually look like

look like a mess so here right here we see this is where we did our experiment this is the amo hutch at the LCLs so

this is the outside looking in so our experiment happened inside here it all has to happen inside a hutch because x

rays are dangerous they can ionize things so they could ionize you so they don't want anybody in there and dancing

around in the X rays I mean it's not like when you go to the doctor and get an x-ray of a bone it's probably more

dangerous so here you can see this is our whole setup so the LCLs beam

actually comes through this tube right here and comes into our this is our experimental chamber that I just showed

you so all of those detectors and everything that I showed you that we're nicely resolved and you could see what was going on well that's this big mess

of stuff right here here we see from a different angle the LCLs goes down this or the the photons go down this tube and

back here is our is our experimental chamber so still kind of messy so here

we can see we have another rendering of what this machine looks like it still looks complicated the lcls beam comes through this way

here's some of our detectors here and here this is our big gas jet that I described so this is this is our

apparatus also drawn see so now you can still see that it's complicated but you can still kind of see it and this is the

control room not to control the entire LCLs but this is the control room just to control this little machine right

here so all of this is dedicated to controlling this machine right here this is a pretty big effort so now remember

this is this ojay spectrum that we just talked about right so we see that this is this is the spectrum that we talked

about we can describe each of these by different combinations of these

electrons the different final combinations of these electrons so I blew it up right here and we can see our

spectrum and now let's overlay the spectrum we got from the lcls and what

do we see we see an extra bump so we've done it we have found this double core hole for the first time ever we have

seen this no one ever before us has ever seen this and we see this bump for the first time so that's really exciting

this was a celebration after we finished this I went to my bosses house and had

breakfast and said we did it so why did we do all of this well remember our

initial problem we wanted to study something about chlorophyll right we or we wanted to study energy conversion so

we wanted to understand the interactions of the parts of this molecule with light so a photon would come in and what

happens we don't know we needed a tool well now we have a tool to unravel the

mystery of energy conversion in nature without destroying the bonds right this is this molecular magic trick right we

have a tool then now we can by pulling the cloth out we can probe each individual bond and see what's going on

right we can see what's going on in this bond what's going on in this bond and we can do it in such a fast manner that we

can do it exit right after the photon hits the chlorophyll and we can probe it so what's next do we just put

chlorophyll in the LCLs well you could some people problems some people do want

to do this they just want to put chlorophyll in there and see what happens but I think all you're going to

be able to study then is still the structure of chlorophyll and not really the function so what do we want to do we

want to take little smaller parts and put those in the LCLs and try to discover the function of all

of that so for example we kind of just studied this little bond right here right just this little part is all we

put in there one little one little line so what should we do next well let's pick another line let's pick this line

or let's pick this line over here or pick your favorite line right you can find your favorite line in this diagram

and you can put it in the LCLs and you can study how it interacts with light and that's what we'd like to do we'd

like to have a tool that we can come up with a function of each little part here and even though nature does it so well

and has refined this process over billions of years maybe we can find a way to do it better maybe by knowing the

function of each little part we can say oh we don't actually need this down here we don't need this and we can find a

better way to do this and we'll have a better way to change a light energy into

electrical energy or even the other way to turn electrical energy back into lights and make better lighting for

rooms or to come up with better ways to solve our energy problems so thank you

very much for listening as I said these LCLs the LCLs is a big machine we have a huge number of people that were involved

and just helping us do our experiment all of these people were actually just involved to help us do our experiment so

it was a big it was a big group of people it was very helpful and I'd also like to thank US Department of Energy

offices of science for giving me funding so thank you very much

well that was a fun lecture very entertaining I'm sure they're a bunch of questions in the audience so we're going

to entertain questions for a while I'm going to ask James to repeat the question when it's asked to the benefit

of the people on the back okay and I'm gonna do this I'm going to be looking at the three different parts so if I don't

be Q now I'm going to pick you in a minute so okay let's start here in the

middle right down here oh well repeat

the question repeat watch how much did it cost to do this experiment well yeah

yeah the LCLs is a user facility so actually for me to ought to my research

group it it didn't cost us really anything other than to pay me to be there to be there all night to sit there

and watch this machine but i think the last figure i heard was that the lcls

cost somewhere around a dollar a second to operate something something like that

when it's turned on so something close to that yeah okay we have we have

another question over there

how does it create so the question was how does it create the stable and unstable bonds so I think you're talking

about these two orbitals where we came together and we made a plus and a minus right so we came so I mean if we just

try to conserve number of orbitals we came in with two orbitals right we had

these two spheres and they came together and now you made two combinations you made a plus combination you made a minus

combination right so we just conserve numbers if if two orbitals go in then

you have to get two orbitals out and these two orbitals have to have different energies and they also have to have a different shape right they can't

they can't have the same shape so and having a different shape this one look

just like an elliptical blob and the other one because it had to have a different shape had two blobs that

weren't connected in the middle so and right because of this this blob that's

connected in the middle pulls everything together and makes everything stable and this this other blob these there's two

of them and there's nothing in the middle pulls everything apart so I guess

I I think I'm answering your question and the the unstable one is actually

just the repulsion of the nuclei whereas the stable one is just pulling together the nuclei because there's all these

electrons in there he had a full up do you have a follow-up yeah the the the 1s

and 2s yes so the the happy face was because

they go into these orbitals that pull the gym okay the happy face was because

we went into these orbitals that pulled everything together just so you're

talking about here okay so write these these two orbitals is lower orbital here

was this one where we we came together and they add them and it's one big blob and this one they came together and

there were two blobs right they were the two separated ones and these are unhappy because the the molecule wants to get

pulled apart now the 2's up here it's also a sphere it does the same thing so

these two orbitals come together and you can add them and you can subtract them

and you get the same blob for down here you get a blah one blob an elliptical

blob and up here you'll get the same kind of shape with two blobs maybe I

have a picture real quickly here of this we can probably do this yeah we can talk

about this after afterwards you came from tiny better I need you to show you on the slide yes on the left yeah you

yeah sorry

the double core hole well so we can do theory we can we can sit down and we can

work out all the equations the question oh sorry he wants to know how I'm sure

that that little that extra little bump in the spectrum the oj spectrum is actually our double core hole so we have

a couple of ways of this one we know what all of the single core hole should look like and so we knew what that

spectrum was so we saw an extra bump so that's that's the first indication that something new is happening with the LCLs

how do we know that it's this double core feature well we can do the equations of quantum mechanics we can

work out all of the math we have a theorist I don't know if he showed up here tonight I don't see him around we

have somebody who sits there and works out these equations and he found way

where the energy of this this feature should be where this decay energy should end up and it matches so we see this

bump right at the energy that we would have expected it to be at so that's our that's another verification that we

think that this is this is this double core hole and we could do further experiments if we won we if we get

another LCLs run we could probably do further experiments to verify this but

right now the fact that it's an added bump from something at the LCLs and the fact that it's at the correct energy

makes us think that it's it's what we're looking for let me try on this side now

and I will come back there now so let me go to the very back

yes

mmm okay so I the question was do these double core holes naturally occur and

the answer is not no you never get

enough x-rays together I mean so under

normal conditions so i would say on the earth or something like the earth maybe

somewhere in interstellar space you could have something like an LCLs going on I don't want to say for certain but

on the earth you never get enough x-rays together at one time to actually have two photons interact in that 750 o

seconds before the the oj DK happens or the oj Meitner decay before that happens

that takes seven femtoseconds so we need to have two photons interact with our molecule before before that can happen

and actually no other x-ray source has enough x-rays no other x-ray source in

the world right now has enough x-rays to make to have to x-ray photons interact

with this molecule before the decay can happen look at that answer that's okay

okay let me take another question here on the right

right okay so the question was why does the valence stay in place why doesn't

the valence get blown away by the x-ray since they're more weakly bound ok so

the to answer that there's there's some theory that goes behind this but I'll try to explain it as best I can so

nature is a lot like car manufacturers car manufacturers are very bad at making

fast cars but they can make slow cars very well by the same token nature is

really good at making slow electrons and really bad at making fast electrons so it doesn't like to make fast electrons

so if the x-ray photon came in and ionized the electrons from the core or

from the valence the extra energy of the valence would actually be given to the

electron is a kinetic energy and it would make a very fast electron but nature really doesn't like to make fast

electrons so x rays mainly interact with the core electrons does that answer your question yeah yeah yeah he does have a

more sophisticated answer you can come down afterwards and he will tell you the details let me get someone in the middle

here yeah sorry you're just went into

the other let's do both of them okay so ladies first

okay so all right I'll try out the question was how does getting rid of the

core electrons allow you to study the valence environment okay uh so I'm

hoping that this doesn't get too difficult I do have some slides that I could talk to you later about if you want to do that but so you can think of

these cores as being isolated things right so they're they're positive charge surrounded by the negative charge of the

electrons so if you remove a core electron right removing a negative

charge is similar to adding a positive charge so what we could think about now is we have these cores that now we

remove a negative charge from each one or we add a positive charge to each one so now these two things are like two

positive charges so if you have two positive charges close together they're they're not happy they want to be

further apart so we see a shift in energy of these core levels so we'll see a shift in energy of this ojay electron

so if they're further apart they're happier so the oj electron since it's happier the oj electron will have more

energy so if they're close together and they're unhappy the oj electron will have less energy um that that might be

confusing about why when they're unhappy the oj is less energy i could draw you a picture and it would probably make more

sense if you'd like me to do that later let's take a question here

um so I think they're there are certain equations oh sorry is chlorophyll better

at I'm sorry I keep forgetting that they lure feel better at converting light energy into electronic energy than say

our state-of-the-art photovoltaics and I would say the two processes are very

different I think if we could I mean the goal of these organic materials would

actually be that they would be easier to produce then these photovoltaic devices

that we have now so the silicon devices are kind of expensive to produce they

also have some some nasty by products that are produced and hopefully if we

were to I mean this is many levels off right many levels of study off the goal

of the of making these organic things would be that they could be more

efficient they would probably be lower cost to make and they would probably not have the same byproducts that the the

normal photo via take the the silicon devices would have and I think in

depending on I mean when we study the function of each part we could find that maybe we can do it more efficiently than

in state-of-the-art silicon can do it we're going to take two more questions from that side and then we're going to

close and the questions can continue afterwards but we need to get closure and get going so we have here in the

front yeah the gentleman glasses yes

to measure down to okay what kind of technologies did we need to measure down to a femtosecond okay well so you can't

actually so there's no electronics or anything like that that can measure down

to a femtosecond so usually how you would go about measuring time scales like this in a laboratory setting would

be to use light and you would overlap based on overlap of light pulses you can

start to measure down to femtoseconds because remember the speed of light so

if you look at how far light goes in a and a femtosecond it it's something that you could start to measure maybe not

with a ruler but with a very precise measuring instrument so that's how you how you usually measure down to such

these short times as you use light and you do some sort of interference between life to measure down to these short

times you can probably give you a more detailed explanation afterwards I think

it will be helpful the last question the top over there okay so the question was

besides studying chlorophyll what other applications does this double core whole technique have well this double core

whole technique will let you study any molecule any molecule you can think of if you want to know about the bonding or

what's going on it will let you study that so if you if you're interested in a

certain reaction or a certain thing that's going on in a molecule these

double core hole should be able to study it right they're very fast so they're they're good at for being your your

flash right in your stroboscopic and imaging because they're very fast to create and they don't live very long so

they're a very quick flash and they're also since they're sensitive to the separations between atoms and the the

bonding between the atoms but it's a good tool to study any kind of chemical

that that you're interested in if there's any process that you ah run that you're not sure about you

could probably start to study it with these double core holes you have to develop a lot more technology probably

but you could probably do it to any molecule James told me that he will be

available for autographs down here further questions drawings everything

you want so let's give him a big round of applause for this fantastic

SLAC National Accelerator Laboratory