Gas phase chemistry is important to many environments on Earth and beyond. The Earth’s atmosphere is dominated by free radical reactions that, when perturbed by pollution, can lead to serious environmental problems like stratospheric ozone depletion and urban smog. Outside Earth, many other planetary atmospheres are affected by gas phase, radical chemistry, including the atmosphere of Saturn’s Moon Titan. Gas phase chemistry in interstellar clouds can synthesize the molecular building blocks of our universe. Studying gas phase chemistry has also led to basic chemical knowledge of how chemical reactions proceed and how intermolecular forces work.
This work is dedicated to studying gas phase chemical reactions with high-sensitivity laser spectroscopy. Laser spectroscopy can be a sensitive and selective way to detect gas phase species. Since laser pulses can both create reactants and detect the products, laser techniques allow the study of chemical kinetics in real time. Consequently, many different laser techniques have been developed to study gas phase chemistry. This thesis is divided into two sections: a longer first section on my work at the California Institute of Technology in Pasadena, CA and a smaller second section based on my work at the Université de Rennes 1 in Rennes, France. These two sections, while on different topics – atmospheric chemical reactions and collisional rotational energy transfer at ultra-low temperatures – are united by their study of gas phase with laser spectroscopy, which shows the breadth of this experimental approach. This thesis will both look at kinetics (the rate of chemical reactions) and product yield of chemical reactions, both key pieces of information to modeling gas phase reactions.
The first part of this work outlines my work at the California Institute of Technology, studying atmospheric radical chemistry with cavity-ringdown spectroscopy (CRDS). Chapter 1 put this work in a broader picture of current scientific work on Earth’s atmosphere. Chapter 2 provides a detailed description of our cavity-ringdown spectrometer and temperature-controlled flow cell. Next, I discuss work on three important atmospheric reactions: the isomerization of simple alkoxy radicals (Chapter 3), the reaction of HO₂ with NO (Chapter 4), and the reaction of OH with NO2 (Chapter 5).
The second, and smaller, part of this work, contains one chapter – chapter 6 – on work done at the Université de Rennes 1, which describes work on the rotational energy transfer in collisions between CO and Ar at temperatures from 293 to 30 K with infrared-vacuum ultraviolet double resonance CRESU experiments. </p
