Vibrational relaxation in atom-exchange reactions. Classical trajectory study of Cl + HCl and Cl + DCl collisions

Abstract

A classical trajectory study has been carried out to investigate the dynamics of Cl + HCl (v= 1) and Cl + DCl (v= 1) collisions, where these are restricted to a single potential hypersurface. Calculations were performed on five LEPS potentials ranging from one with a moderately high barrier (+26.0 kJ mol^–1) for H or D atom transfer to one with a moderately deep well (–25.9 kJ mol^–1) with the three atoms in a linear, symmetric configuration. On all these surfaces, vibrational relaxation occurred predominantly in collisions where the trajectory passed at least once through the symmetric (r_AB=r_BC) configuration, and rate constants have been calculated both for transfer of molecules to v= 0 and for atom-exchange. Comparison with the observed rates of de-excitation of HCl (v= 1) and DCl (v= 1) by Cl atoms suggest that if energy transfer occurs principally in electronically adiabatic collisions then the barrier for H atom transfer must be lower than has been previously supposed.