What do I do? 4: Infrared Spectroscopy in France

When people find out that I am doing a PhD in Chemistry, they often ask, somewhat foolishly (by those who aren't really that interested), what it is I do.  I then find myself in a position of trying perform a juggling act to find the balance between a number of things.  How in detail do they want me to go?  Where's the right place between talking over their head, and sounding like a condescending jerk.  Are they actually interested, or are they just being polite.  Based on their background, what parts will they find most interesting?  On top of that, I need to plot a coherent course through my thought process so that if they are interested, they don't get lost in the maze inside my head.

So, I've decided to write it down, and see if I can make a logical series of articles about what I do, starting with the background information that's needed, eventually ending up on what I do day to day. Today I'm going to talk about infrared spectroscopy and synchrotron radiation.

I started to write this, and realized that I really should break my 2 main projects in France into 2 (or 3) different posts, so that they don't get too long. This one will be about the project that I've been working on periodically while I've been here.  The principal investigators (PIs, a term that you should read to be a fusion of my boss/head scientist/adviser/person who gets the money so I can do science, but don't always understand the details of what I do) that I work with here had "beam time" on the SOLIEL Synchrotron, so we spent most of January, and then a few days here and there since working over there and making use of that facility.

If you're not familiar with what a syncrotron is, it is a type of particle accelerator designed to be used as a light source for various experiments (it's a really big lightbulb in the spectroscopy post's diagram).  Electrons are accelerated to a significant portion of the speed of light in bunches, which are then stored in a ring with electronics and magnets that keep them flowing in a circular path around the synchrotron (the storage ring at SOLEIL is 113 meters in diameter, which is about 371 feet for my american friends.  That's just a little longer than a football field).  While the particles velocity is constant, at every bend in the ring, they "accelerate" as they change direction, which causes them to release energy as light.  This light is directed to the beamlines, which then use it for various scientific purposes, such as spectroscopy.  Light from the beamline is very intense, and covers a large range of wavelengths, so it can be filtered to make it useful source for many applications.  The link to SOLEIL has some pretty good diagrams to help visualize this process, so check that out (I realize the website is in French).

Image of a fraction of the storage ring and facilities of the beamlines from the catwalk above it inside the synchrotron facility.  

The beamline that I got to work on specializes in infrared spectroscopy.  You may remember from previous posts that infrared light typically corresponds to difference in energy levels between vibrational states of molecules.  We're interested primarily in molecules that have been, or may be detected in space, and so all of our projects revolve around that.  While some of the stable molecules that exist on Earth can also be found in space, there are also many unstable and highly reactive molecules in the interstellar medium, and so we need a way to produce those in the lab.  For the set of experiments I've been doing here, our method for synthesizing radicals is to produce a plasma inside a cell, which in turn promotes some crazy chemistry, and produces fragments of the original species, as well as reactions that create molecules through recombinations of the original atoms.

 I've included a couple of pictures of what that plasma looks like, mostly because I think they look awesome.  Inside plasma (which is a state of matter), you get all sorts of crazy chemistry, and energy is being released, and so it gets very colorful.  The color the plasma turns is dependent on the molecule the plasma is formed from, and recently the plasma we've been producing in the lab has been orange.  The one pictured here was our injection of ammonia, hoping that we could strip off a hydrogen and make NH2, then measure it (spoiler warning: we could). 

Raw data before treatment

The lab here is very interested in this characterization of molecules, in the pursuit of assisting in their detection in space, so that's what the purpose of our experiments here has been.  I'm extremely interested in building instruments to make that possible.  While I was at SOLEIL, I was excited to learn about the synchrotron source, get to help set up and optimize the experiment for performing both stable measurements and discharge measurements, then get to work on the data

Data after treatment

analysis of this data.  One of the things I spent a lot of my time while we were at SOLEIL doing (because once we're set up and optimized, the computer does all the actual data acquisition) was working on writing scripts in python to clean up the data, and perform some of the analysis.  A problem with raw data is that there is a lot of information inside that we don't really want that originates with electronics, optics, and other parts of the measuring equipment, rather than the thing we want to study.  On the right is an example of some of the data, and what I did to help clean out those pieces of information that we didn't really want.  The data here is a combination of both vibrational spectroscopy and rotational spectroscopy.  We call it rovibronic data.