Orientation effects in Cl+H2 inelastic collisions: characterization of the mechanisms

Based on quantum mechanical scattering (QM) calculations, we have analyzed the polarization of the product hydrogen molecule in Cl + H-2 (v = 0, j = 0) inelastic collisions. The spatial arrangements adopted by the rotational angular momentum and internuclear axis of the departing molecule have been characterized and used to prove that two distinct mechanisms, corresponding to different dynamical regimes, are responsible for the inelastic collisions. Such mechanisms, named as low-b and high-b, correlate with well defined ranges of impact parameter values, add in an essentially incoherent way, and can be clearly differentiated through the quantum mechanical polarization moment that measures the orientation of the products rotational angular momentum with respect to the scattering plane. Other directional effects turn out to fail when it comes to distinguishing the mechanisms. Quasiclassical trajectories (QCT) calculations have been used as a supplement to the purely quantum mechanical analysis. By combining QM and QCT results, which are in very good agreement, we have succeeded in obtaining a clear and meaningful picture of how the two types of collisions take place.