Full quantum vibrational simulation of the relaxation of the cyanide ion in water using the Ehrenfest method with quantum corrections

Abstract

The Ehrenfest method with quantum corrections is used to describe the vibrational relaxation of the cyanide ion in liquid water. All the vibrational degrees of freedom of the system are described using quantum mechanics, including the normal modes of each individual solvent water molecule. The remaining translational and rotational degrees of freedom are described classically. Two different relaxation pathways are identified, one V-V and another V-TR. The V-V pathway involves the participation of the bending mode of the water molecules. This pathway is the fastest (T(1)(a) approximately 20 ps) and is also the most important, accounting for approximately 82% of the relaxation process. The other V-TR relaxation pathway involves the direct transfer of the CN(-) vibrational quantum to the rotational and translational motions of the solvent and is significantly slower (T(1)(b) approximately 180 ps). The agreement with the experimental measurements is shown to be excellent.