Rotational polarization of reaction products and reprojection of angular momentum

Abstract

Molecular beam experiments employing electric deflection analysis of reactive scattering show that the rotational angular momentum for CsBr from the Cs + HBr reaction is strongly polarized perpendicular to the initial relative velocity vector. Similar polarization is observed for the K + HBr, Cs + HI, and Cs + CH3I reactions, but none is discernible for Cs + Br2 and Cs + CCl4. The experimental method involves comparing deflection profiles measured with the field oriented parallel and perpendicular to the plane of the reactant beams. It is shown that the difference between these profiles depends primarily on <cos2 x>, where x is the angle between the rotational angular momentum and the initial relative velocity vector. A sudden, non-adiabatic change of quantization axis corresponding classically to ‘reprojection’ plays an important role in the experiments. This process provides another measure of <cos2 x>. The values found for <cos2 x> range from ⪷0·05 for the K + HBr case to ⪷0·21 for Cs + CH3I, as compared to <cos2 x> = 0 and 1/3 for delta-function and isotropic distributions, respectively.