Collision-Induced Dissociation by Helium: A Piecewise Construction of the Cross Section

Abstract

Molecular dynamics calculations were performed to simulate the collisions between a helium atom and either a water dimer or various geometries of the Na(H 2 O) 3 + cluster. The trajectory calculations were interrogated to document the partial conversion of the collision energy into internal excitation of the cluster. Owing to the small size of helium, the collision energy, which is transferred as an impulse to the cluster, is deposited initially on one of the atoms of the cluster. The amount of transferred energy in the atom that is collided depends of its mass, and more interestingly if it is involved in a H-bond like bonding with a water molecule. The general rules that have been drawn to describe the energy transfer allowed us for a picewise construction of collision-induced-dissociation cross sections, each piece being the energy tranferred toward a specific atom of the cluster. This offers a framework for extracting quantitative information on binding energies from collision-induced-dissociation experiments by helium in M(H 2 O) n + systems (M is a metal atom). Importantly, the fit to the experimental data that is allowed by the present model is not restricted to the threshold energy region of the CID cross section. An application is given for the He + Au(H 2 O) 1 , 2 + collision.