Imaging photon-initiated reactions:: A study of the Cl(2P3/2)+CH4→HCl+CH3 reaction -: art. no. 094301

The hydrogen or deuterium atom abstraction reactions between Cl(P-2(3/2)) and methane, or its deuterated analogues CD4 and CH2D2, have been studied at mean collision energies around 0.34 eV. The experiments were performed in a coexpansion of molecular chlorine and methane in helium, with the atomic Cl reactants generated by polarized laser photodissociation of Cl-2 at 308 nm. The Cl-atom reactants and the methyl radical products were detected using (2+1) resonantly enhanced multiphoton ionization, coupled with velocity-map ion imaging. Analysis of the ion images reveals that in single-beam experiments of this type, careful consideration must be given to the spread of reagent velocities and collision energies. Using the reactions of Cl with CH4, CD4, and CH2D2, as examples, it is shown that the data can be fitted well if the reagent motion is correctly described, and the angular scattering distributions can be obtained with confidence. New evidence is also provided that the CD3 radicals from the Cl+CD4 reaction possess significant rotational alignment under the conditions of the present study. The results are compared with previous experimental and theoretical works, where these are available. (C) 2005 American Institute of Physics.