Some recent research successes

Doing research is not a good way to get instant gratification for what you are doing. It’s an arduous process that involves collecting and interpreting data in search for answers to specific questions. This can be a very lengthy process that involves checking, re-checking and starting all over again. It can be frustrating, demoralizing, and just plain difficult. Hence, when it pays dividends you feel not just invigorated but absolved.

Lately, I’ve been feeling pretty good to tell you the truth.

Since I started working at Synchrotron SOLEIL with the DESIRS beamline a year and a half ago, I’ve been involved in numerous projects and this year my publication rates are experiencing a bit of a boom.

Recently I wrote a few words about the first publication of mine from the work I’ve been doing at SOLEIL, but since then I have had three more works published in the past couple of months (two as first author). Since my writing for this site has been rather slow, I wanted to write a little bit more about the projects that led to these publications and provide a brief and general introduction to the kind of work I have been doing. These three recent publications  I want to highlight (all of which you can find and download under my Publications list), touch upon three different facets of research, namely combustion chemistry, astrochemistry, and atmospheric chemistry.

Combustion chemistry

Article name: Valence-Shell Photoionization of the C4H5 Radical.

As the name suggest, combustion chemistry deals with the chemistry of combustion processes. I.e. chemical reactions at very high temperatures that involve combustible species; mainly hydrocarbons. As our civilization is wholly dependent on combustion processes that fuel an enormous transportation industry that includes cars, airplanes, ships, etc., understanding the exact chemical processes that take place when energy is harnessed from fuel, is very important.

One of the very first reactions chemistry students learn about is that of combustion where a hydrocarbon reacts with oxygen to produce carbon dioxide (CO2) and water (H2O). This is a gross piece of oversimplification albeit to serve a noble pedagogical purpose. The exact nature through which the hydrocarbons break down is very complex and involves a myriad of unstable molecules and radicals that quickly recombine to form larger and larger molecules of soot, on top of the aforementioned CO2 and H2O.

One of the radicals that is of significance in these combustion processes is 2-butyne-1-yl which is an important precursor in reactions that lead to soot formation in flames. We studied this radical in terms of its spectroscopy as well as another very important physical property. Namely its photoionization cross section.

A cross section is the property of a molecule that describes an area around the molecule where the chances of it interacting with a photon is very high. Think of it as how big of a bullseye the molecule has on its head. The photoionization cross section describes the size of the area around the molecule where the molecule will capture a photon of a given wavelength and ionize (lose an electron).

Radicals are very difficult to produce in a laboratory setting and hence experimentally obtaining their physical characteristics is invaluable. The cross section of the radical can be used e.g. in large computer models which predict the rates and products of chemical reactions. Without this cross section, these models rely on (almost) arbitrary guesses of the molecules’ cross section or cross sections obtained from theoretical predictions which are not always reliable. This is something we touch upon in the article as a very recent theoretical estimate of the radical’s cross section was found to be off by a factor of eight.

Astrochemistry

Article name: Quantifying the Photoionization Cross Section of the Hydroxyl Radical.

I have written a bit about astrochemistry before so I’m not going to spend too much time setting the astrochemical stage.

Water is omnipresent in the Universe and an important component in the formation of water in space is the hydroxyl radical, OH. Its cation, OH+, reacts very rapidly with H2 (the most abundant molecule in space) and forms ionized water, H2O+, which can form neutral water through a series of recombination reactions that involve neutralization with electrons.

This brings us once again to the photoionization cross section.

Knowledge of how the OH radical interacts with light to produce OH+, is of great importance to understand the chemistry of interstellar water formation. The key property of the radical that gives us insight into this light-matter interaction is the photoionization cross section. This cross section was measured and compared with the result of another study which obtained the cross section by a different method.

As I mentioned earlier, part of science is checking, re-checking and doing it all over again. This is most definitely an example of why that is important. We find that there are still some discrepancies between our values and those obtained by other groups and hence this matter is by no means concluded. This is something we must continue to work and improve upon so that measurements via different experimental techniques converge to a better degree.

Atmospheric chemistry

Article name: Isotope Effects in the Predissociation of Excited States of N2+ Produced by Photoionization of 14N2 and 15N2 at Energies between 24.2 and 25.6 eV.

Atmospheric chemistry is a branch of chemistry that pertains to chemistry of not only our terrestrial atmosphere but of planetary atmospheres in general. Understandably, this is a very wide and diverse field that incorporates meteorology oceanology, volcanology on top of physics and environmental chemistry.

Among the topics covered by atmospheric chemistry is that of charge transfer, where a positively charged ion collides with a neutral molecule and imparts its positive charge onto it. I.e. the collision is hard enough that the ion “steals” one of the neutral molecules’ electrons.

Molecular nitrogen, N2, is the most abundant molecule in our atmosphere. The properties of the excited states of the N2+ cation are of importance to charge transfer effects between He+ and N2 as it may possess a role in the atmospheric escape of He atoms. I.e. He+ ions colliding with N2 can exchange the charge and gain enough kinetic energy to escape the atmosphere.

We studied the spectroscopy of a particular electronic state of N2+ (for both the 15N2 and the 15N2 isotopologues) and measured to what extent the excited state led to a process called “predissociation” which is really just techno-speak for “broke apart”. There is a clear isotope effect observed where the 15N2+ are less prone to break apart at these energies rather than 14N2+. This does make sense as heavier isotopes usually form stronger bonds together. The most striking observation we made was, however, that as soon as 14N2+ possessed the energy required to break apart, it did so in a very unhesitant manner.  A charge transfer between He+ and N2 would thus lead to an unceremonious break-up where the He+ ion donates a positive charge to N2, gains enough energy to escape the atmosphere and meanwhile the N2 immediately dissociates into reactive N+ and neutral N atoms.

It goes without saying that none of this could have happened without all my brilliant co-authors, co-workers, co-…llaborators and co-conspirators. A massive thank you to all of you and here’s to continuing doing some good science.

I think that should about do it for now. This is a bit of a test run to see whether people are at all interested in reading these sorts of short summaries of my research so if you happened to like it, don’t hesitate to let me know. 😊

Ciao.

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