Reaction of Cl with CD4 excited to the second C-D stretching overtone

The effects of vibrational excitation on the Cl+CD4 reaction are investigated by preparing three nearly isoenergetic vibrational states: parallel to 3000 > at 6279.66 cm(-1), parallel to 2100 > at 6534.20 cm(-1), and parallel to 1110 > at 6764.24 cm(-1), where parallel to D1D2D3D4 > identifies the number of vibrational quanta in each C-D oscillator. Vibrational excitation of the perdeuteromethane is via direct infrared pumping. The reaction is initiated by photolysis of molecular chlorine at 355 nm. The nascent methyl radical product distribution is measured by 2+1 resonance-enhanced multiphoton ionization at 330 nm. The resulting CD3 state distributions reveal a preference to remove all energy available in the most excited C-D oscillator. Although the energetics are nearly identical, the authors observe strong mode specificity in which the CD3 state distributions markedly differ between the three Cl-atom reactions. Reaction with CD4 prepared in the parallel to 3000 > mode leads to CD3 products populated primarily in the ground state, reaction with CD4 prepared in the parallel to 2100 > mode leads primarily to CD3 with one quantum of stretch excitation, and reaction with CD4 prepared in the parallel to 1110 > mode leads primarily to CD3 with one quantum of C-D stretch excitation in two oscillators. There are some minor deviations from this behavior, most notably that the Cl atom is able to abstract more energy than is available in a single C-D oscillator, as in the case of parallel to 2100 >, wherein a small population of ground-state CD3 is observed. These exceptions likely result from the mixings between different second overtone stretch combination bands. They also measure isotropic and anisotropic time-of-flight profiles of CD3 (nu(1)=1,2) products from the Cl+CD4 parallel to 2100 > reaction, providing speed distributions, spatial anisotropies, and differential cross sections that indicate that energy introduced as vibrational energy into the system essentially remains as such throughout the course of the reaction. (c) 2007 American Institute of Physics.