HBNI Alumni Webinar by Prof. Swaroop Chandra

[00:00:27]I I think I lost your audio. Oh, okay.

[00:00:31]Perfect. Yeah.

[00:00:32]>> Yeah. Can can we start now?

[00:00:34]>> Yeah. Yes, please.

[00:00:37]>> So, good evening to all the faculty members, students, elimined participants present here in the conference room as well as those joining online through WebEx and YouTube. And good morning to the speaker who is joining us from uh uh Keltech USA. On behalf of HBNI, I warm all of you for today's HBNI alumin webinar. The HBNI alumini webinar is a series for uh initiative of the HBNI aimed to strengthen the interaction among alumini students and faculty member across all the uh DA units as well as alumini stationed outside. The series provide a platform for uh distinguished alumini to share their academic journey, research experience and professional insights while also enabling our students and young researchers to learn from their scientific and career trajectories.

[00:01:38]It is my great pleasure to welcome today's speaker Dr. Sav Chandra who is joining us online from California Institute of Technology Celtech USA.

[00:01:49]Dr. Sup welcome to you. Dr. Sup Chandra completed his integrated MSE in chemistry from Amrat Vish Vishov Vidyapit pour and subsequently joined Isizikar Kalpakam where he pursued his doctoral research under guidance of Dr. N. Ramatan and Dr. K Sundar Rajan. His PhD work at HBNA focused on use of matrix isolation infrared spectroscopy and quantum chemical methods to investigate nonquivalent interactions including subtle intermolecular interactions such as hydrogen and nicogen bonding. Following his doctoral work, he joined the research group of professor Michael E. Brown at Keltech where he is currently engaged in research at the interface of chemical physics and planetary science. Today he is going to speak on science of look and tell infrared spectroscopy in chemical physics and planetary science. Matrix isolation is a powerful technique in which molecule is trapped in inert gas matrix and uh studied in this. This is a very uh powerful technique where where the inert gas and molecule are trapped at cryogenic temperature and then uh one can study the uh intramolecular interactions, transate species, subtle changes in the molecule bonding. In recent years uh people have done this with the photosis in the lab as well as the advanced radiation source such as synretton radiation uh where which has opened the possibility uh for simulating astrochemical and planetary environment in the laboratory.

[00:03:33]In today's lecture Dr. Supchandra will show how infrared spectroscopy a powerful tool for molecular science can be applied in two very different research domains. First to understand septile molecule interactions through matrix isolation spectroscopy and quantum chemical calculations and second to investigate the chemical and geological of extraterrestrial and interstellar space IC surface through laboratory and science experiments. We are delighted to have Dr. Chandra with us today and we sincerely thank him for accepting our invitation to deliver this HBNA alumin webinar. I hope Dr. Sup is clearly audible and visible to all the audience uh present online and he will be delivering the talk from uh USA. Dr. Sorukar welcome to you for today's webinar. May I now request you to kindly deliver your talk. Thank you.

[00:04:36]>> Thank you so much for that introduction.

[00:04:38]It's a real pleasure to be back. Uh I hope I'm audible. Uh >> yes, you are audible.

[00:04:46]>> Okay. Uh let me share my screen.

[00:04:57]So uh is it now visible?

[00:05:01]H >> yeah your screen is visible.

[00:05:04]Okay. Uh and the slides are moving.

[00:05:07]>> Yeah. Moving, moving, moving.

[00:05:10]>> Okay. Perfect.

[00:05:12]Okay. So, uh good evening everybody. Uh thanks a lot for this opportunity to uh Pamjit sir and of course Ramnadan sir for uh thinking of me. Uh so let's uh to get started. So this image that you see here is uh the surface of Europa which is a Galileon moon um which orbits Jupiter. It's uh there so there are four Galileon moons of Jupiter uh Io Ganymede, Europa and Kalisto. Uh where Europa is the second furthest away from Jupiter and it is also the smallest moon. They're called Galilian moons because they were first seen by Galio himself. Uh these pictures are taken by Galio the space probe in 1995. So we'll get to Europa in a few minutes. But uh as promised uh I am here to uh talk about how uh uh the work I did in my PhD and how it eventually um the how how the how I got connected to the planetary science community in the first place because it's it wasn't obvious to me that I could do something like this before I uh applied to applied to uh Professor Brown's group. Uh so anyways so uh I hope the this slide is visible and uh so here as uh Pamjits mentioned uh the PhD work was focused on uh studying the chemical physics of uh a weak non-coalent interaction uh called the nikoen bond. Um is my pointer also visible?

[00:06:59]>> Yes s is visible.

[00:07:00]>> Okay. Thank you sir. Yeah. So uh what we are talking about so the entire PhD was focused on uh studying the basic chemical physics of the nikcogen bond which is actually an analog of the well-known hydrogen bond but then uh with a key difference. So uh what I've shown here in these cartoons is uh a a normal uh coalent bond that would exist between say a hydrogen atom and a relatively electronegative atom and assuming that this is the shape of the electron density uh around hydrogen which gets donated or you know which participates in bonding. So what happens is due to the electro negativity of this species you have a partial positive charge that is generated on this end.

[00:07:55]Basically the electron density is polarized and that leaves the hydrogen open for additional interactions with electronrich species or nucleophiles. So a similar thing is observed in case of a nicogen atom. A nogen atom is any atom in the nitrogen family. nitrogen, phosphorus, arsenic, antimony and bismouth. The reason why it gets interesting is that uh by nature these uh uh atoms are supposed to be electronrich but then once they form a coalent bond again a similar phenomenon of the polarization a directional polarization of the electron density depending on uh the electro negativity of the bonded atom and also in what direction it is bonded there is a polarization that is generated on this end. So in in uh effectively what it causes is it uh creates a dichotomy in what in the species that can approach the bonded nicogen atom. So atoms that I mean um entities that approach via this region would be electronrich while these planks would be open to electron poor species. So this gives rise to curious reactive uh uh in I mean reaction pathways and we believe these are responsible for the initial uh control in the diffusive phase of most reactions uh involving the nitrogen family of atoms. So the goal was to first off isolate the uh isolate uh significant experimental evidences for the existence of such bonding. So the idea was uh instead of studying the uh nikcogen interaction between the uh between the atom and the uh atom of the other molecule which is interacting the effect of the nicogen bonding on the non-coalent bond itself would be analyzed. Now it would manifest as uh given that the bond order or the total bonding capability of the nicogen needs to be conserved when uh if it part when it participates in a nicogen bond there is an effect on the coalent bond that already exists within its molecule. So the strength of that uh the uh there will be a change in strength of this coalent bond which will definitely be visible in the vibrational spectrum of this larger molecule uh wherever the nitro uh nicogen atom belongs. So the idea was to track the change in the strength of that non-coalent uh the track the change in strength of the coalent bond and then trace it back to nicogen bonding itself. Um so how we do that is where the technique of matrix isolation comes in. So the change in bond length due to nicogen bonding is going to be very small and therefore the change in strength also is going to be pretty small. Therefore the change in the vibrational frequency of the bond also is going to be small or minute. Now to detect that shift in uh absorpt uh the vibrational frequency from its you know undisturbed state uh one would need to have a better resolution compared to say the solid state. So this is for uh this is to show you a comparison. Uh these these are spectra of uh carbon dioxide in various forms. So the this trace here that is seen is of solid CO2 uh CO2 ice while the green traces here as well as uh here both these things are of ga gaseous CO2 of course uh there is also a little bit of C13O that we can see um but then the point is in both these scenarios the vicinity of the major absorption of CO2 is heavily congested In the case of gas phase, these are row vibrational excitations of the CO2.

[00:12:17]While uh in the solid phase, it's the intermolecular interactions between CO2 itself. But then when we dilute CO2 in a non-reactive gas uh such as nitrogen in this case and the dilute gaseous mixture is deposited on a coal substrate what we get is a thin film in which CO2 is isolated from other CO2 molecules and so most of the intermolecular interactions all of the intermolecular interactions are uh eliminated and given that CO2 is no longer moving or it has uh no rotational degrees of freedom. Uh the major uh spectroscopic broadening effects which are pressure and uh Doppler broadening they get cut down and in effect what we get is a very nice sharp resolved feature of the carbon dioxide and this is the asymmetric stretch of CO2 that we see here. So this leaves the spectral region in the vicinity open for us to measure the change in uh measure the minute changes in the uh vibrational bond strengths. Uh when the when a molecule participates in nicen bonding. So for nicogen bonding we made use of two uh key molecules as models. Uh one was phosphorus trichloride and the other was uh nitromethane. both of which uh contain phosph uh one which contains phosphorus and the other which contains uh nitrogen. Um so that's how the PhD went.

[00:13:52]So how did we do matrix isolation? I will focus on that because that is what uh uh leads me to the next part of the talk. So this is the facility where uh I learned the craft I can say and uh to zoom in uh this is where all the fun happens. So uh what we see here is a cryostat which is uh uh which which basically cycles helium gas and uh the helium gas under goes a compression and expansion cycle and what happens is it uh compressed helium is fed somewhere right about this point and there is a cold finger from which helium extracts heat for its expansion phase and once it expands it is cycled back into a compressor and Then you know the cycle goes on. In effect what happens is the cold finger is you can achieve temperatures uh uh up to 4 kel at this point uh inside this uh little chamber.

[00:14:53]And uh the cold finger is enclosed by a vacuum chamber which is what you see here the gray uh colored box and it is also equipped with windows uh which will allow passage of IR light. So the gas mixture that I just told you about is dep uh deposited on the cold finger here and then we pass infrared light through the uh IR transparent window and the matrix itself and we collect the signatures which is how we get the uh spectrum.

[00:15:23]So this is IR spectroscopy of matrix isolated species and that this is the equipment. So someone who has worked in worked with this equipment can can basically handle uh cryogenic spectroscopy over a wider uh scale and that is the connection for what I'm uh connection with what I'm doing currently. So expert I mean experience with the previous equipment allows me to work with this equipment which is the uh which is our lab here at Caltech right now. Uh again zooming in. So this is our vacuum chamber again. Uh okay I okay I'm sorry I miss mis mentioning the vacuum part uh previously. So the cold uh for the cold finger to achieve the low temperatures uh uh a high vacuum is required around it to prevent uh you know heating. So the helium cycle helium uh triacooler keeps evacuating heat from the cold finger but unless we cut down the atmospheric heating surrounding the cold finger it it would be very hard to achieve equilibrium temperatures below 77 Kelvin because at 77 Kelvin the dominant component of the atmosphere nitrogen starts condensing on the cold finger and you one achieves an equilibrium there. So to go below 77 Kelvin and also for uh a healthy functioning of the cryostat the uh cold fingers are always housed inside a vacuum. This is a primary uh requirement. The vacuum is also required to ensure the purity of our samples. So vacuum is a prerogative for uh in both these uh you know uh low temperature systems. So here uh in the new in the setup that we use here at Caltech for uh planet uh in what we call the planetary ice chemistry lab uh or pickle uh in short. So uh here this is the vacuum chamber which is at the center of the lab and uh all experiments happen inside this and basically uh this forms the center of our exper uh all our analytical uh ventures. So the vacuum chamber here uh and if uh there is a slight uh red spot that is visible here that is where the sample sits and the key difference in this system as opposed to the matrix isolation system is that in the matrix isolation system light passed through the sample matrix and so we what we did was transmission spectroscopy while in this case what we're doing is reflectance or to be specific diffuse reflectance spectroscopy. Now why is diffuse why the change is because the lab basically okay let me uh let let me quickly say what the lab enables and then go ahead. So it's a vacuum chamber into which a solid bulk sample can be put in and it can be taken down to uh low temperatures as low as uh 12 Kelvin or uh well in some cases 10 Kelvin even and so in under when holding the uh sample at those conditions we can perform INC2 infrared spectroscopy and UV spectroscopy. So you have uh the uh infrared spectrometer sitting over there. We channel the beam out, send it into the chamber, collect it out into the detector. We can get the spectrum.

[00:19:04]Um and a an additional capability is for an electron radiation with an electron gun which is what you see here. Uh it's the input beam line of the electron gun here. So coming back to the question why the switch from transmission spectroscopy to diffuse reflectance because um compared to transmission spectroscopy in diffuse reflectance uh light is incident on a substrate and then gets reflected radially in all directions. So unless one collects all of the reflected light the signal to noise ratio of the spectrum is going to fall compared to the transmission spectra. Despite that why do we do diffuse reflectance is because the spectra that we get in the lab need to be comparable to the spectra that we uh get from the telescopes. Uh so this forms the uh main purpose of the lab. So uh this is where the original body that I showed you uh Europa comes back. So Europa is the prime focus of the lab. Uh all of the experiments are centered on understanding the surface of Europa and through understanding the surface of Europa what happens beneath the surface its origin its evolution uh and all that. So how does how do how do we get data or how do we look at this is where the title becomes relevant. Uh it's literally the science of look and tell. We look at Europa or any other uh planetary object. Uh looking basically involves uh analyzing the sunlight reflected off of the surface of uh the body. And we one can do two things with the reflected sunlight. one can do one can use it to construct an image. One can split it across the wavelength domain to get a spectrum. So uh the uh planetary ice chemistry lab works in the second domain. We do the spectroscopy of reflected sunlight off of the surfaces here specifically of Europa. So these are the uh prime two uh state-of-the-art instruments that are currently used.

[00:21:28]This is the James Webb Space Telescope and this is the Hubble Space Telescope.

[00:21:33]Um the James Web Space Telescope works in the uh works right from uh 1 microns or okay uh 10,000 wave numbers uh all the way to 400 wave numbers and even lower u while the Hubble space works in the UV visible regime. So basically what you have are telescopes with spectrometers connected which are in space. Now what is the difference between being in space as opposed to uh being on ground? The groundbased telescopes have been the workhorse of observational astronomy for many years uh uh before uh Hubble went into orbit for the first time. So the main problem with ground telescopes or the yeah the main problem would be the presence of the atmosphere. So a big swath of the spectral bandwidth is blocked out by water vapor um carbon dioxide and other components in the atmosphere which are not transparent in the IR or in the UV base. So well one cannot do UV spectroscopy on ground because thanks to the ozone layer um and so that is the advantage of having space telescopes. So coming back what uh fine we get data from telescopes and uh we analyze that uh we get spectra but then the spectra that we get are essentially lines or uh specific signatures of molecules uh in the corresponding states that they exist. Now given that the molecular states that we're studying are quite different compared to the states that they exist on earth or the libraries that we have created. It is necessary that we make conditions uh compatible or comparable to or as close to the surfaces that we are studying. Now given that most of the surfaces in the solar system with very few exceptions are airless or they do not have an atmosphere there is no greenhouse effect on these surfaces which means the temperatures these surfaces hit are uh extreme. So depending on the distance from the sun and the exposure to sun uh these surfaces can go from downright cryogenic conditions to uh very uh hot conditions like uh temperatures exceeding au,000° centigrade for example on Mercury while the other end of Mercury which faces away from the sun plummets to sub-zero temperatures. So uh so low temperature conditions under vacuum is a general criterion for most surfaces across the solar system which is where the lab comes. Now getting specific to Europa, a little bit of history before I get into Europa.

[00:24:39]Excuse me. Um so like I said uh Europa is called a Galileon moon because it was first observed by Galio the astronomer uh in the 17th century. And so uh this is Galileo's notebook uh where he sees that the big circle which is Jupiter has three dots and at time at times a fourth dot appears and what he saw was uh the dis of Jupiter and the four dots they move together across the sky. Now this was revolutionary in that time because the world was still geocentric or the world still believed that earth earth was earth was at the center while the sun moon and everybody else orbited the earth. this uh this instance of Jupiter and its uh four dots uh which later were found to be moons uh with the moons orbiting around Jupiter and them moving together al across the sky without uh the earth as the center. This shifted this caused a major shift in from geocentrism to helioentrism. Of course it didn't happen immediately. uh we know what happened to Galileo because of that. But uh this is the uh historical signific significance of it. Um and this here is a image that was captured by one of my friends here in uh yeah 2023. So sure we can definitely see what Galio saw even today. So to to zoom in a little more a little closer to Europa the moon.

[00:26:22]Uh this is again photographed by Galio the space probe this time. Uh these are images from 1995. So uh and this is pretty unusual for a object. For example, our moon is uh dark. It is um it is it has a lot of mountains. It has a lot of craters. Uh compared to our moon, this surface is pretty smooth in terms of lacking craters. Like one can one can see one lone crater at this scale. Uh there there are there are a couple of more smaller craters, but that's it. Compared to that, the surface is pretty crater-free, which is unique.

[00:27:06]Uh and then there are these stripes and characteristic colorations that we see for a spectroscopist. the these are all of great interest. So these are some uh higher resolution images that were returned by Galio uh during its flybys.

[00:27:22]So what we see is it's a generally white surface which is which appears to be contaminated or you have black gunk that lies around and uh when you look at the color images from afar you also have shades of red you also have shades of yellow. Of course, these two images are stretched in terms of contrast uh uh to to to you know to better make out the colors. Uh these this image I would say is uh closest to reality.

[00:27:56]So uh and well I'm an infrared spectroscopist first off. So what does the infrared spectrum of this look like?

[00:28:05]That is how uh uh uh this is an infrared spectrum of Europa surface collected by Galio's uh near infrared mapping spectrometer uh the NIMS. And uh I'll I'll come back to these uh uh different traces that we see here in a minute. uh now we saw a lot of stripes and uh we also said uh I mean we also saw that there are uh close to zero craters on Europa at least compared to other objects. So these three effects uh these three phenomena that uh are central to Europa's evolution and the way it is uh uh so it is important to understand these phenomena. So one thing is you have Jupiter at the center and you have three you have the three moons Io which is at the the innermost Europa the second innermost and uh furthest away is Ganymede. We of course have Kalisto outside which hasn't been shown here.

[00:29:12]The reason is these three moons are logged in what we call uh resonance as in uh it's it's it's pretty obvious from the graphic right uh uh Io completes four orbits for every two orbits completed by Europa which is in turn uh for every single orbit of Ganymede. Now why this is important is because over time whenever a body gets pulled into orbit around uh around a center of mass over time the orbit tends to gets circularized and what that means is the orbiting body will have the same amount of gravitational force acting on it all the time. But then because of this resonance that exists between Io, Europa and Ganymede, neither of their any uh none of their orbits are perfectly circular. They are all slightly elliptical. So what happens is their distance between Europa I mean the the distance between Jupiter and themselves keeps changing depending on their location which in turn changes the gravitational force that is acting on them. And what that causes is it basically stretches and compresses the object. Uh when it is closer to Jupiter, the uh faces that are uh closer to Jupiter get pulled strongly while the faces that are away from Jupiter are uh pulled a a little less strongly. So what you have what you have is a sort of a stretching and compression of the uh body itself. what that causes and the the phenomenon is called tidal kneading and what it causes is it heats up the body from inside and it forms a local heat source. Um this is important in the case of Europa because until until Europa and say uh other some of the other moons were uh discovered there uh the assumption for liquid water to exist in solar system was purely dependent on the distance between the sun or the star itself for other solar systems and the planet or the body that we're considering. And so there was this goldilock zone uh which is basically a equilibrium distance from the sun where the temperatures are neither too uh cold or nor uh nor very hot for water to exist as a liquid. And liquid water is treated as a primary condition for uh to you know to for life as we know it. and uh finding life as we know it on other bodies has been a central uh inspiration for most of these uh studies. That's how it get it gets connected. So this is the uh the tidal effect because of the mean motion resonance. Another thing that was noticed by Galilio uh when it flew close to Europa is that um it had a magnetometer uh uh to to uh sense the magnetic field around Europa as it flew by. So what is seen shown here is two sets of magnetic field lines a green field line and a can colored field line. The green field line they change or they they keep fluctuating in strength and direction with a period of 11 hours which fits with the orbital period of Jupiter itself. And so this is induced magnetic field because of Jupiter which is uh which is expected.

[00:32:56]But then what is interesting is the secondary magnetic field which seems to be originating from Europa itself because its period is not in phase with the magnetic field of Jupiter itself.

[00:33:09]And so this how do we create magnetic field? One way is to have moving charges. And given the strength of the magnetic field here, the moving charges need to be very uh they they cannot be very deep beneath the surface of Europa.

[00:33:27]Uh they have to be close to the surface of Europa. And this is where we come back to our IR spectrum. So what we see here is the uh lab spectrum of water ice. Uh the diffuse reflectant spectrum of water ice or snow basically just snow. So the red trace is the lab spectrum. If we compare that to what we see on uh uh if we compare that with Europa's infrared spectrum, it isn't very different. uh the general pattern says that the dominant component of the surface is water ice. So clubbing that with clubbing this knowledge that the surface is dominantly water ice of course with some contaminants and uh the fact that Europa is tidily heated from within and also that Europa has an intrinsic magnetic field right beneath it beneath its surface which indicates some moving charges. Putting these three things together, the assump uh the uh very a very strong belief right now is that there is a ocean of water, liquid water that exists beneath the icy surface of Europa that we see here. And that is what makes Europa all the more interesting because suddenly we have life supporting conditions at distances we never expected in the first place. So that is why Europa becomes important. Um yeah. So obviously uh when when when one wants to study life, one has to look at the chemistry and uh so far all the chemistry that has been done about Europa could be condensed into the identification of these four elements uh hydrogen, carbon, oxygen and sulfur.

[00:35:25]These form uh four out of the six um primary elements considered necessary again for life as we know it. Uh nitrogen and phosphorus are yet to be found. Um but yeah we have these three element uh we have these four elements on Europa. Uh which uh so how do we know that? Um again hydrogen and oxygen come from primarily water. We also have indications of carbon dioxide in the infrared spectrum uh from Galilio. This has again been confirmed by very recent spectra from the James Web.

[00:36:02]Um and then again carbon dioxide with oxygen and then uh sulfur. So the red reddish uh patches that we saw here uh that we see here these are called uh these are said to be sulfates of some kind. Uh it is seen that when um the when sulfurous species are irradiated uh we get they turn red in presence in presence of water ice. So experiments have been done with sulfuric acid, experiments have been done with various kinds of sulfate salts. So while we do not know what kind of sulfates these are exactly, sulfate annion is pretty clear.

[00:36:49]So that is what leads to the presence of uh sulfur also. So these are the four elements that we know. And so coming back to the function of pickle u we have carbon, nitrogen, sulfur and oxygen. So what are the possible chemical cycles that are uh uh you know uh that could be acting there. So uh we figure out uh we we just mapped out a cycle here. This is this is purely a hypothesis. So what pickle does is it goes and tests out each of these chemical pathways that are possible. And for this as a as was mentioned in the abstract um the water ice shell uh there are contaminants which we know is carbon dioxide and some sulfates. But then you uh what is the uh there is also another uh evidence a pretty recent evidence uh which is of sodium chloride that has been found on Europa. So um so based on the three confirmed evidences one is uh sulfates one is carbon dioxide and the third one is sodium chloride all of which contaminating the dominant water component.

[00:38:13]um inorganic salts become very important to Europa. If there is sodium chloride, we we talked about uh the presence of a liquid ocean beneath the surface and all this points to an active presence of inorganic salts in addition to sodium chloride. What are those salts? We have many uh hypothesis but uh other than sodium chloride none of these are confirmed so far. So that is the gen this uh hypothesis of chemical cycles is what lies at the center uh of the focus of uh planary ice chemistry lab as of now.

[00:38:56]Um so I'd like to present one specific result that we have t that we have had in the recent times and uh this is something I worked with directly so I can explain the this better. Uh so here what we saw uh what we see is uh a James Webb space uh telescope spectrum which was acquired uh pretty recently in uh 2022 and what we see here is water again very much what was seen by uh the Galileo NIMS spectrometer and but then given the greater spectral resolution that uh James Web offers the original CO O2 feature which was seen as a single absorption actually was resolved to a double in fact a triplet if one play uh if one pays close attention to this. So there are at least three different absorptions of carbon dioxide uh in within the broad carbon dioxide absorption of uh Europa.

[00:40:07]Now first off the main surprising element here is how does carbon dioxide exist as a solid? I mean uh because we don't see any row vibrational absorption. So this isn't carbon dioxide gas. This has to be solid CO2. Um solid CO2 sublimes at temperatures greater than 80 kel for the vacuum conditions that exist on the surface of Europa. But then the surface temperatures of Europa are me uh measured to be somewhere between 90 to 100 120 Kelvin. So that is the first piece of the puzzle which is how does solid carbon dioxide stay stable enough on the surface to give this to give these absorptions. Now again uh solid carbon dioxide itself the absorption here is uh again this is a this is a difference uh spectroscopy done done by astronomers is in the wavelength uh reg uh wavelength domain as opposed to wave number domain which uh chemists are more uh uh familiar with. So the conversion is pretty simple. It's just 10,000 divided by the wavelength gives you wave number. So the 4.27 27 absorption. This is specific to solid carbon dioxide, carbon dioxide ice. Uh and so that existence is surprising. But then what is the second feature or the third feature over here?

[00:41:36]What are these due to? What states of CO2 do these correspond to? So there are two uh hypothesis uh which is that it could be uh it could be CO2 which is trapped in water ice. It could be uh CO2 which is implaced from outside or it could be CO2 which is landing from space onto the surface of Europa itself. Now what we see uh this is where the uh this this is a map of global map of Europa of course one hemisphere of Europa where the intensity of these CO2 absorptions are mapped over and so if you see we have CO2 concentrations specifically in this equatorial range and specifically in this mapped out regions. Now these mapped out regions are uh are are interesting because unlike the general generally smooth ice shell of Europa uh with you know the characteristics striations and everything. These marked regions are places where ice seems to have broken up or you have you have uh large sheets of ice which appear to be floating or which appear to have been disturbed in the recent times. uh and so one uh broad hypothesis of why these broken ice regions or they're called as chaos terrains exist on Europa is that this is this is a mark of the icy surface being constantly recycled with the material from the ocean that lies beneath the ice shell. So, and then the concentration of CO2 on these regions specifically makes it even more likely or it's not likely for uh astronomers anymore. It is pretty uh clear that uh the CO2 that comes uh that is seen on Europa has to come from within Europa and not from outside. So, this is called as endogenic. The CO2 is endogenic to Europa.

[00:43:54]Um so given fine then if it comes from within Europa then we can have two possibilities again two broad possibilities which is that CO2 dissolved CO2 from car the ocean comes up through the ice shell and that is what we see on the surface. uh or it could be carbon based material. It could be carbonates. It could be organics which from the ocean finds their way to the uh find their way to the surface and then are processed on the surface to give CO2 again. Both these phenomena are possible. So how do we figure out which is which? So the experiment a set of experiments that we did tried to address this. So what we did is it's a it's a schematic of uh Europa's ice shell and the subsurface ocean. It's a I'm sorry it's not a schematic. It's just a illustration. Um what we So the first uh part of the hypothesis which is CO2 dissolved in the ocean making its way through the ice shell to the surface. If that were the case, how would we simulate the uh pressure temperature conditions surrounding every molecule of CO2 that passes through the ice shell and emerges on the surface. What would those what would that change look like? So that is what we tried to simulate as uh simulate in the experiments here. What we did is we have we took a simple pressure chamber which can hold u uh pressures of up to uh 150 bars uh of CO2 and we filled the uh pressure vessel with water and then we uh flushed it with CO2. So that phase basically is replicative of an a an ocean which is hyper concentrated with CO2 and following that what we do is so this is the pressurization of CO2 in water. Following that the uh the entire uh pressure vessel is cooled in a in a regular uh refrigerator to -4° C at at which point -4° C has to be the coldest uh point of liquid water but also the warmest point of ice which corresponds to this little location or the ocean ice interface which could exist on Europa.

[00:46:35]Following that you cool it further to -15° C which is because um we have a lot of dissolved CO2. So our collleative properties say that the uh melting point of water would could be depressed a little. So to make sure that the freezing is complete, we take it down to -15° C and then what we do is we immerse it in liquid nitrogen and when it so there is a further cooling.

[00:47:08]So as you move up through the ice shell there is a temperature decrease. Uh why would that make sense? Because again going back to the tidal heating phase, tidal heating generates heat from the center and that's why you have a uh layer of water. So as you move up you get cool colder and that is exactly what the experiments replicate. And then what did we do? We uh release the pressure of uh release the pressure take out take the ice out grind it up and record the spectra.

[00:47:43]What we see this is for uh CO2 dissolved in water. Uh we pumped in about uh seven yeah seven bars of CO2 and uh what and then do this procedure and then we uh collect the ice, grind it up, make snow out of it and then look at the uh diffuse reflectance spectrum in the IR.

[00:48:08]uh what we see is we get a double instead of a singlet. But then the problem is unlike the band centers of CO2 that were absorbed on Europa which is the which is what the dotted lines show. This is the result of the experiment that we see. Now the James Web spectra are have error margins smaller than five decimal places which means this shift in wavelength is real.

[00:48:39]So the spectrum that we see in the lab is not the same as the spectrum that we see on Europa. So the CO2 that exists on Europa is not of this state at least.

[00:48:52]Now I also mentioned the uh detection of sodium chloride on Europa which means a much closer thing to do would be to do the same experiments with salt water instead of pure water. Does that cause any change? Not really. There is no there is no shift in the uh carbon dioxide wave wave I mean the wavelength positions of the bands. So another thing that we did is instead of CO2 passing through the ice till gradually, it can come it could come out as uh you know cryo volcano uh cryo volcanics or uh plumes of water from the ocean directly coming out onto the surface or from pockets within the ice shell itself. Basically liquid water rapidly condensing at the surface.

[00:49:45]That's exactly what we did.

[00:49:49]we uh pressurize water with CO2 and instead of freezing it gradually we freeze it directly on a liquid nitrogen cooled substrate and then we went ahead and looked at the spectrum. Now comparing the red trace which was from the previous set of experiments, the slow freezing experiments, the flash freezing experiments which is shown by the black gives you a significantly different absorption signature. And uh one could say that uh if one were to linearly combine or you know do other means of convolution for these two things, one could in principle make the features that were seen on Europa.

[00:50:35]But then these two phenomena by themselves do not explain uh the CO2 that is seen on Europa. So what with these experiments what we concluded is it is less likely given the simplicity of these experiments there could be many more uh uh intricate pressure temperature phenomena and also it need not be pure ice. So given the simplicity of these experiments, it makes it less likely that the carbon dioxide that we see on the surface of Europa is dissolved CO2 from the ocean coming up directly. It is more likely that it is carbon based material that is coming onto the surface which is later on processed to be converted into carbon dioxide. This is the uh simple conclusion that we drew.

[00:51:30]But uh the idea of presenting this was uh and yeah so uh this was uh this was uh uh this is a overlaying of what we did. The the pressure temperature changes that we subjected the samples to is overlaid onto a phase diagram a PT phase diagram of uh carbon dioxide and water. And so what you have is that some of the pressure uh pressures of CO2 that we pumped into the liquid fall within the clatherate formation regimes. What are clates?

[00:52:06]Uh they are carbon dioxide hydrates.

[00:52:10]Carbon dioxide with um something analous to water of crystallization. So the uh carbon dioxide hydra uh so some of the pressure regimes that we uh worked in could have given us uh carbon dioxide clates which is what these these clear dlets correspond to but what exactly is this uh shifted feature we still don't know.

[00:52:38]So uh the idea of press uh giving this uh uh experiment was that it is uh spectroscopy is a great tool to analyze and recreate conditions uh and immediately reconcile them with uh telescopic observations. But what is also required in planetary ice chemistry is uh specific preparatory routines for samples because it is not simply the conditions in which we observe these we also have to try and recreate the evolution of these materials. So uh planet uh laboratory science as far as planetary science is concerned requires sample prep methods which are also specific to the objects that we study in combination to the spectroscopy that we do. So I I I hope I uh conveyed some uh bit of information and it was worth your time. Uh I'll be happy to take any questions if there are. Uh thank you so much.

[00:53:58]Uh sir, I think you're muted.

[00:54:05]>> Thank you Dr. Sup uh for a presentation.

[00:54:08]Uh talk is open for discussion.

[00:54:22]Hello sav.

[00:54:25]>> Yes sir.

[00:54:25]>> Hello.

[00:54:27]Basically uh u what I wanted to ask you is like H2O plus CO2 if you're adding form carbon H23 which is acidics. we all know from our standard books. So then H+ and this uh HO3 negative this HO3 negative is having IR spectra which you are uh uh showing or uh it is something other thing because definitely the species form will be at CO3 also getting >> definitely >> we we we do not Yeah. Yeah. uh we we did compare it with uh the uh existing spectra of H CO3 minus the complication there is um so one we we dissolve CO2 in water but then we freeze it out so CO uh H2 CO3 exists as H+ and HO3 minus in the liquid phase it's basically analous to a dissolved solute or a salt but then it has to be kicked out once the entire solution freezes out. This is this is just a hypothesis because the uh uh when we compared existing spectra of HO3 minus with what we see, we didn't see any of the features. Why I mention the complexity is because there are experiments where people did uh co-eposition of H2O and CO2. They make mixed uh films of H2O and CO2 and then produce HO3 in C2. That's one way we have uh spectrum of HO3 minus in the solid phase. Uh but that doesn't fit with what we see here.

[00:56:09]So I think uh I mean but this it doesn't mean there is no HO3 minus. It's just uh far below detection limits probably.

[00:56:17]>> Okay. Okay.

[00:56:18]>> Yeah.

[00:56:18]>> And one uh this just curiosity what what will be the density of Europa uh dense? Great question.

[00:56:29]We all know that Jupiter is I think in gas state now almost gas.

[00:56:33]>> It is it is dominantly I mean uh it is a few uh thou 100 kilometers of gas but then it has a solid core but uh uh yeah what we see is all gas. Yes.

[00:56:45]>> Okay. What what about this Europa? Uh >> the density of Europa uh the density of Europa is uh very close to uh actually only slightly more than that of water rice which is surprising. So uh uh to be honest I I need to I need to check the number. Let me check the number.

[00:57:09]>> Just say like my son was also asking that time one time.

[00:57:14]>> Yeah. And and one more question like what will the vacuum atmospheric pressure on this Europa?

[00:57:21]>> Uh sorry sir correction for that. It is it is actually 3 g per cc. But then why is it uh why is uh why it make why it is interesting is because uh the space probes that uh went around Europa uh with by tracking the gravitational anomalies one can actually map how the density distribution might be inside uh from the core right up to the man uh you know the mantle and the ice shell that we see. So the topmost layer of water ice that we see and the subsurface ocean they constitute to a very small part of Europa's uh total uh you know uh mass.

[00:58:03]So that is that is actually an evidence against uh the presence of subsurface ocean but which is which is you know which is countered by the weak magnetic field. I'm sorry I just wanted to clear out uh yeah >> thank you. Thank you. Thank you. I'm sorry sir you had another question though I interrupted I was what what is the pressure the atmos atmospheric pressure on Europa >> on the surface >> like huh on the surface like on the moon is around 10^ - 12 or 13 atmosphere >> it's it's very similar to that it's very similar to that uh what we have is a very thin exosphere of uh uh water um carbon dioxide primarily Because you have because of the magnetic field of Jupiter, we have charged particles constantly bombarding onto the surface and they sputter material off of the surface. So the thin exospherics uh that we see is primarily the uh sputtered material but otherwise it's it's uh UHV uh 10 theus 12. Yes.

[00:59:12]>> Okay. Thank you. Thank you very much. SO have you seen the photosis part also to compare with the >> great question actually uh >> yeah uh so for the CO2 uh studies we haven't done photosis so far uh because one challenge that we had was um these experiments that we did uh involving CO2 in ice we did these as rough at rough vacuum uh now rough vacuum is fine fine as far as partial pressures of CO2 are consider considered at rough vacuums itself we hit very low partial pressures of CO2 which are comparable to Europa but to do photosis and also electronic irradiation we needed to do it in our original chamber which I showed you initially >> uh the problem was by the time we put the sample into that chamber there was so much of intermittent thawing that all the CO2 just passed out so we haven't done photosis experiments so far But photosis is important in uh another uh it was it was a key consideration for uh establishing sodium chloride's presence. Uh so the yellow coloration of sodium chloride u on irradiating it with electrons. It's a known phenomenon from the 1950s.

[01:00:34]So that was matched with the yellow coloration on the uh European ice shell.

[01:00:42]again because of uh irradiation. But then what was also seen is the yellow coloration is because of this color center which is produced in irradiated sodium chloride. You have free electrons uh in chloride anion latises. But then the color centers that are produced are also quenched when exposed to broadband sunlight. And so what you have is a equilibrium between uh the production of color centers on the night side but then as soon as it comes to the day side it gets quenched. So you have an equilibrium and um we replicated experiments in the lab to measure the uh you know rate of production and we could actually correlate it directly with uh what we what has been observed by uh the Hubble space. So that that is how uh we confirm that it is sodium chloride because looking at colors or even looking at specific spectral band centers is not enough because we can have multiple species having coincident band strengths uh band centers.

[01:01:47]>> Uh just have you also are you also planning to concentrate on this uh experiment? You have used CO2 plus H2O mainly but maybe some interests are there in ammonia or formic acid they are also uh the in elementary molecules.

[01:02:09]>> Yeah also people have done lot of work.

[01:02:12]>> Absolutely. Absolutely. So uh here uh for that um the main challenge ammonia they're all under consideration like I said none of these have been eliminated yet the challenge is to have clear signatures of it uh with why why is challenging is um the dominant contribution being water ice on the surface the 3 micron region here is heavily dominated by the water ice absorptions itself. So any organics that we expect to see will have to appear somewhere here while the ammonia absorptions would have to appear somewhere here. So uh this is the challenge with detecting it. People have done experiments with ammonia and there are actually there is actually one paper which postulates the uh presence of ammonia on Europa but uh it is not yet uh unambiguously detected is what I would say ammonia is there acetylene and uh organics are are we we are we are a little more behind because again a major thing sir is uh we are only beginning to get midair data uh dominant amount of data that we get is NI for all these things and so for organics the only range we have is uh further of uh you know 3.2 2 microns which is heavily shadowed by water ice. So that's the existing challenge but people are working on it.

[01:03:53]Uh thank you very much uh Dr. Dr. Srup Chandra for insightful and engaging lecture on behalf of honorable vice chancellor and dean and uh all the community of HBNI students and faculty I sincerely thank you for delivering today's HBNI webinar and for sharing your insightful journey and research so beautifully with us because uh this field itself is a fascinating field and your lecture provided the um fascinating prospects of how A powerful spectroscopic technique can connect two different domain of research molecular chemical physics and planetary science.

[01:04:37]Your discussion on matrix isolation spectroscopy chemical calculations and laboratory planetary science was highly informative and intellectual enriching for all of us. I am sure that the students faculty members present here and participating only through online uh platform have greatly benefited from your talk and from the insight you shared with both the topics. We are tr truly grateful for your time, your valuable contribution and your continued association with HBNI. We hope to remain connected through your lectures in future also whenever we request you and uh we hope to see more advanced experiment from your uh laboratory on this uh topic because you have already gone to the advanced days uh compared to your PhD program and uh hopefully you we would also like to see the experiments on uh uh advanced because this is a basically uh uh understanding the uh nature of uh interstellar space and uh you are very well actually on that line and the field is never uh complete this field as at least on the scientific domain. Thank you once again Dr. Zup for this excellent uh lecture. I also thank all the faculty members, students and participants who joined us today both in person and online and contributed to making this webinar a meaningful and successful event. With this we conclude today's HBNA webinar. Thank you all.

[01:06:18]Thank you.

[01:06:19]>> Thank you.