Kinetics of the Gas-Phase O(1D) + CO2 and C(1D) + CO2 Reactions over the 50-296 K Range.

The kinetics of the reactions of CO2 with atomic oxygen and atomic carbon in their first excited singlet states have been studied at room temperature and below using the Laval nozzle reactor method. O(1D) and C(1D) atoms were created in situ by the 266 nm pulsed laser photolysis of O3 and CBr4 precursor molecules, respectively. While O(1D) atoms were detected directly by vacuum ultraviolet laser-induced fluorescence at 115 nm, C(1D) atoms were followed indirectly through a chemical tracer method. The measured rate constants for the O(1D) + CO2 reaction are found to be in excellent agreement with earlier work and extend the available kinetic data for this process down to 50 K. The present work represents the first kinetics study of the C(1D) + CO2 reaction below room temperature. Both reactions display rate constants that increase as the temperature falls, with a more substantial rate increase observed for the O(1D) + CO2 reaction. This finding could be due to the increasing lifetimes of the intermediate species involved at lower temperatures.