Time-resolved studies of free radicals and laser-initiated chain reactions

The reactions, energy transfer, and dynamics of free radicals produced by ultraviolet laser photolysis were studied. The measurements on free radical chain reactions, absolute rate coefficients, and photofragmentation dynamics were carried out by time-resolved infrared emission spectroscopy. The dynamics of hot methyl radical reactions reveal that translational excitation is essential in the rate enhancement of several of these reactions. The partitioning of reaction exoergicity into vibrational excitation of the polyatomic products of methyl radical reactions is also studied. Some first rate coefficients are obtained for deactivation of the antisymmetric stretch mode of vibrationally excited methyl radicals with a variety of partners. It is shown that the vibrational and translational temperatures in a laser initiated chain reaction differ substantially over the course of the chain. The photofragment emission spectrum of vibrationally and rotationally excited CO and CH3 produced in the photolysis of acetone is obtained. It is shown that laser multiphoton ionization of N2 is an alternative means of probing vibrational and rotational temperatures in combusting mixtures.