A low temperature, high pressure kinetic study of chlorine reactions critical to determining stratospheric ozone destruction

Chlorine plays a significant and often dominant role in the depletion of stratospheric ozone, particularly in the polar region. The kinetics of many important chlorine reactions is still poorly understood at stratospheric temperatures, and this work is designed to address this issue.; Harvard's High Pressure Flow System is the experimental apparatus used to study these reactions. This system is specifically designed to operate free of heterogeneous wall reactions, making it ideal for low temperature studies. Sub-ambient temperatures are achieved on this system for the first time, and the use of the resonance fluorescence technique allows for the kinetic study of chlorine reactions over a wide pressure and temperature range.; The Cl + CH4 → CH3 + HCl reaction represents the key sink for stratospheric chlorine. Kinetic data in the relevant low temperature range (180-220 K) is sparse due to experimental constraints and extrapolation is dubious due to non-Arrhenius behavior. The data reported here range from 170 to 298 K, enveloping the entirety of stratospheric temperatures while also representing the lowest temperature measurement ever recorded for this reaction. We report a bimolecular reaction rate constant significantly higher than that currently recommended by the Jet Propulsion Laboratory's (JPL) data evaluation at low temperatures; we expect that this will lead to a revision of this important rate.; The ClOO + NO → ClNO + O2 reaction is an important side reaction in instruments that use resonance fluorescence to make in situ measurements of ClO, the primary form of activated chlorine. Little data are available for this reaction, so it is studied here at temperatures ranging from 170 to 198 K. The rate obtained falls within the range that is predicted based on the data from the in situ instrument stated above. The rate of the termolecular reaction Cl + NO + M → ClNO + M is required to determine the ClOO + NO rate, and is measured from 170 to 298 K. The results confirm this reaction's pressure dependence while also extending the rate's low temperature limit.; This laboratory flow system's ability to operate at lower temperatures than any other comparable system opens up a wide range of future research directions. Experiments that can be conducted are discussed along with potential modifications and improvements.