Effect of translational energy on the reaction Li + HF(v = 0) → LiF + H

Abstract

In a crossed molecular beam study we have measured double differential cross sections for the reaction Li + HF(v = 0) → LiF + H at collision energies ranging from E_tr = 88 to 378 meV. With rising E_tr the angular distribution of LiF in the center-of-mass frame changes from nearly forward–backward symmetric to preferred forward scattering. The mean relative recoil energy of the products amounts to approximately 50% of the available energy with a slight tendency to decrease with rising E_tr. Our findings agree well with results of quasiclassical trajectory calculations based on the potential energy surface of Laganà and co-workers. The calculations suggest that the change of the scattering characteristics is caused by the significant dependence of the differential cross sections on the rotational enery of HF rather than by the transition from a long lived complex to a direct mechanism. The present findings are consistent with the results of an earlier crossed beam study obtained employing significantly different experimental techniques and data analysis procedures (C. H. Becker, P. Casavecchia, P. W. Tiedemann, J. J. Valentini and Y. T. Lee, J. Chem. Phys., 1980, 73, 2833).