Velocity dependence of the excimer rotational alignment in the reactions of Xe* with halogenated methanes

Abstract

Using a beam-gas time-of-flight technique, the XeX* (X = Cl, Br, I) rotational alignment from the reactions of Xe( 3P 2,0) with CH 3I, CH 2I 2, CH 2Br 2, CHBr 3, CBr 4, CHCl 3, and CCl 4 are reported. The degree of product alignment varies markedly between these systems, decreasing with collision energy, halogen mass, and number of halogens per molecule. At the lowest collision energies studied, a transition from positive to negative polarization was found for CBr 4, CHCl 3, and CCl 4. The negative polarization corresponds to the preferential alignment of the product rotational angular momentum vector parallel to the relative velocity vector.