Recent progress in infrared absorption techniques for elementary gas-phasereaction kinetics

Sensitive and precise measurements of rate coefficients, branching fraction s, and energy disposal from gas-phase radical reactions provide information about the mechanism of elementary reactions as well as furnish modelers of complicated chemical systems with rate data. This chapter describes the us e of time-resolved infrared laser absorption as a tool for investigating ga s-phase radical reactions, emphasizing the exploitation of the particular a dvantages of the technique. The reaction of Cl atoms with HD illustrates th e complementarity of thermal kinetic measurements with molecular beam data. Measurements of second-order reactions, such as the self-reactions of SiH3 and C3H3 radicals, and determinations of product branching fractions in re actions such as CN + O-2 rely on the wide applicability of infrared absorpt ion and on the straightforward relationship of absorption to absolute conce ntration. Finally, investigations of product vibrational distributions, as in the CN + H-2 reaction, provide additional insight into the details of re action mechanisms.