Collinear proton transfer in a symmetric bihalide system

Abstract

A semiclassical vibrationally adiabatic theory is applied to the collinear gas phase proton transfer reaction Cl − + HCl → ClH + Cl −. It is found that tunneling is negligible in the reaction and that the principal dynamic features are governed by the deep potential for the reactants. Evidence is presented that quasiclassical trajectory dynamics is unreliable for this collinear system, in that the trajectories exhibit marked nonadiabaticity - i.e. complex formation in which there is significant energy transfer between the proton motion and the relative motion of the two chloride ions. It is argued that, by contrast, the quantum collinear reaction is adiabatic and direct in character. Comparison with recent experimental results suggests that development of a full three-dimensional theory may be necessary for an adequate picture of this reaction.