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yeah so I'm Jake roll and a student here

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at the University of Colorado in the

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vitae group I'm actually just across the

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way from here but I'm going to move into

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the solar system and talk more about

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Earth and Venus and about some

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photochemical formation of aerosols why

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we care about those and some work that

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I've been doing on sulfur chemistry with

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sulfur dioxide and so just to give you

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some background about why we care about

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sulfur sulfur has been observed in a

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number of planetary bodies including a

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number of the rocky planets as well as

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some moons Jovian moons and I'll be

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focusing on Venus and Earth and kind of

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the implications there and so sulfur is

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really important for climate and for

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understanding the temperature of our

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planet the energy budget the reason for

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this is in any sort of oxidizing

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atmosphere most of the sulfur that gets

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released ends up is sulfur dioxide then

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three reactions with 08 radicals goes on

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to form this HS 03 ultimately you end up

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with this so3 and threw a water

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catalyzed reaction you get so pure

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sulfuric acid and sulfuric acid is

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really important because it's this

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hygroscopic molecule it likes to take up

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water and form aerosol which is this in

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this case an aqueous droplet suspended

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in the air so in Earth's atmosphere in

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the lower atmosphere in the troposphere

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where there's a lot of water what ends

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up happening is you seed cloud and you

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get rain out and that soul and so then

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most of its depleted however in the

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upper atmosphere where there's a lot

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less water that so2 tends to stick

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around you get much higher

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concentrations of so2 and that aerosol

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rather than raining out stay suspended

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for a number of years and thus what this

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is really important because it can

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reflect away a lot of incoming solar

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radiation and change the temperature of

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the planet

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and so in earth we actually end up with

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this young galere which is a layer of

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aerosol that you can see at about 15 to

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20 kilometers in the atmosphere and you

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can see that it actually reflects away

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quite a large amount of light and

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anytime that there's a large eruption on

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earth that injects large amounts of so2

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into the stratosphere we see these large

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changes in optical depth where an

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increase in optical depth means that

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there's more light being scattered away

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and these sorts of events can have you

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know fractions of a degree Celsius

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change on the planet overall temperature

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but so if we go to Venus Venus tells us

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something pretty interesting because

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there's huge amounts of sulfur and

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Venus's atmosphere about from 50 to 70

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kilometers there's this large sulfuric

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acid clouds that cover the entire planet

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but interestingly starting at about 90

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kilometers there's a huge increase in

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so2 and sulfur monoxide concentration

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several orders of magnitude change and

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this actually exceeds any model

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predictions by multiple orders of

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magnitude and so what this tells us

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there's probably some sort of chemical

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formation of so2 in the middle

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atmosphere of Venus but what's really

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interesting about this is that these

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conditions are very similar to Earth's

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stratosphere mesosphere and when I'm

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talking about these conditions I mean

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temperature water content and incoming

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solar flux and so one of the things that

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the models have done to try and account

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for this is to implement this infrared

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visible fatalis asst of sulfuric acid

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that was some work done in our group o

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number of years ago and so in the case

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here what happens what's interesting is

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this is potala sis on the ground

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electronic state you're exciting a

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vibration this o.h stretch to the v

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equal for v equals 5 level and when that

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happens that hydrogen starts to hop

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across the molecule and can jump from

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one oxygen to another and in the case

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where it jumps to the oxygen that

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already has an o H you get photolysis

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and leading to so3 and water and when

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you're at the high altitude arm in the

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atmosphere where there's a lot of UV

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I'd available that s 03 then immediately

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photo Liza's to form s 02 so this is a

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photochemical source of so2 in the

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atmosphere however this doesn't even

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begin to account for the amount of so2

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that's observed in Venus's atmosphere

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and so the models do a couple of other

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things to then try and compensate and

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account for this that may or may not be

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physically accurate one of which is they

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include an inaccurate UV cross-section

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so they take the upper limits of

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measured cross sections from about 200

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to 300 and 20 nanometers and assume that

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all the light absorbed immediately leads

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to Fatah lysis although a lot of work

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that's been done has shown that this

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cross section actually is probably much

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smaller and is not actually leading to

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any sort of UV photolysis another thing

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they do is they include red light

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fotosis of the sulfuric acid monohydrate

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where the sulfuric acid molecule is

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complexed with a water molecule this

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does lower the barrier for this reaction

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however there is one problem with that

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and that a lot of work that's been done

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looking at this has shown that instead

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of leading to photolysis instead what

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happens as the energy goes into breaking

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these hydrogen bonds and leads to

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dissociation of the cluster rather than

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fatales as the sulfuric acid so neither

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of these things are likely to be

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actually happening in the atmosphere so

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this has led to us to ask the question

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of if we look at the entire system of

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so2 is there something else is there

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another reservoir some other molecule

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that could be photo lysing and leading

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to so2 in the atmosphere and so one

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thing that we started to look at is

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sulfurous acid h2so4 an h2 so4 and this

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is an interesting molecule it's tricky

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for a number of reasons it's never

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actually been observed in the gas phase

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and a couple of reasons for this is that

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h2s 03 is energetically uphill so so2

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plus water is energetically much more

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favorable to go down

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as well as you pay an entropic price for

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making h2s 03 as well as you go from two

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molecules to one and there's this large

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barrier to forming it so you need to get

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over the barrier and format and as you

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add more and more water you drop this

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barrier however when you drop that

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barrier it's much more likely for it to

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then fall apart and make so2 instead and

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so we've been looking for other ways to

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try and make this molecule and I've done

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some theoretical work with Jamie

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Donaldson and so you'll know I've kind

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of swapped directions here from s 0 to

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plus water to making the acid it's about

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five kcal per mole uphill you have this

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large barrier about 35 kcal per mole

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however there is this excited electronic

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state for so2 so it's this triplet state

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that you can excite to when you're there

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in a collision of water a relatively

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mild collision you can create this

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complex that then inner system crosses

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back to an excited singlet state which

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are just two different types of

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electronic states and then that singlet

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state can then proceed forward to make

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sulfurous acid and so this is a

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potentially new pathway to try and make

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this and so one thing I'd like to know

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is this triplet state is actually a

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forbidden transition you'll note that

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this is a spectrum x 500 so it's

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actually forbidden to go from the ground

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electronic state to that triplet state

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however there is this large singlet

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state absorption in so2 from about 250

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to 300 and 10 nanometers and there's

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been a lot of work done showing that you

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can excite this state and then that

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rapidly inner system crosses to the

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triplet state which can then go on to do

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reactions and so in my experiments we

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excite with a xenon arc lamp that's

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filtered so this filter shows that we

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cut off at about two hundred ninety five

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nanometers the reason why we do that is

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because we're trying to avoid exciting

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this state over here this is a

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photoactive state where so2 photo liza's

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to form sulfur monoxide and i'm excited

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oxygen atoms so we really wanted to

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avoid initiating

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any sort of chemistry with that so in

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our system we use this filter xenon

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light and then in at a right angle to

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that we have a green laser going through

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the system that we then detect and

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anytime you form any sort of aerosol

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that laser beam then gets scattered and

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you can measure a depletion in the laser

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intensity and show that you're actually

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making aerosol and so here you can

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actually see pictures of our experiment

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you can see that we have this green

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laser light going through this is with

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the lamp on when you have the lamp off

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you actually can't even see this laser

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beams you can see that there's a large

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amount of scattering of light and so

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then to give you something that's a

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little more quantitative if we have just

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water in the cell we turn on the lamp at

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time zero you get no depletion same

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thing if you have just so2 as soon as

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you have any sort of mixture you get a

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depletion and as we increase the ratio

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of so2 to water we get a larger

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depletion so we are forming aerosol

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through some sort of acid formation so

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one question we wanted to really make

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sure of is this oh h chemistry this

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traditional o-h chemistry in our

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atmosphere we want to make sure that

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wasn't happening so a common thing in

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atmospheric experiments is to use

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cyclohexane as an o H scavenger to react

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with all of the o H that's potentially

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there and remove it from the system

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there's just one problem with this it

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turns out the so2 if you have

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cyclohexane as soon as you excite and

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you end up in that triplet state it

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rapidly reacts with cyclohexane to form

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aerosol even faster than you do with

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water so it fills the cell with this

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iridescent cloud and there's not a lot

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that we can do about that we did do

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experiments with cyclohexane and just

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water to make sure that there was no

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aerosol formation and we don't see any

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aerosol formation there so we relatively

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sure that there's no o H chemistry going

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on however we can't include this with

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the so2 in the system and so instead a

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turn to a kinetics box model so a

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relatively simple kinetics box model but

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one thing to point out is that it is

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possible through s 0 to s 0 to

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collisions

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we can make so3 that would go on to form

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sulfuric acid and so we look at this so3

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collisions using the side bottom at all

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collisional deactivation of this triplet

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state we assume that some fraction this

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branching ratio leads to a formation of

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acid and so if we assume that the

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branching ratio is a hundred percent we

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can see that this blue line is sulfurous

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acid in either case far out competes the

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formation of sulfuric acid and in the

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lower concentration so2 where you

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decrease those s 0 to s are two

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interactions we actually lead to an even

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larger increase and so if we instead

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look at the ratio of sulfurous to

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sulfuric acid formation you'll note that

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you do not need to have a branching

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ratio of a hundred percent if we go to

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these much lower concentrations of so2

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where I've now done some more

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experiments of that you can even have a

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branching ratio of one or two percent

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and still outcompete that formation of

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sulfuric acid and so with that I just

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like to acknowledge my group and sources

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of funding and thank you guys for your

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time and I'd be happy to take some

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can you resolve differences in stable

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isotopes of sulfur species

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spectroscopically um so with our system

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we cannot I don't have the ability to

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look at different isotopes however I'm

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definitely interested in doing some mass

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spec experiments where depending on the

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mass spectrometer we might be able to

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actually look at that this is definitely

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that triplet state that inner conversion

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from the singlet to triplet state does

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depend on the mass of the sulfur

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isotopes and so it will lead to a sulfur

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mass independent pretty experimental

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work but for the I guess the

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observations that you're doing um so the

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observations were done with Venus

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Express I know they definitely can't

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unfortunately yeah other questions all