Spectral grid study of ro-vibrational coupling in hydrogen-metal scattering

Abstract

A theoretical technique is presented that allows one to quantum mechanically describe the rotational and vibrational behavior of diatomic molecules that experience nonegligible ro-vibrational coupling. Such situations arise when molecules have a strong electronic interaction with a metal, leading to variations in the bond length, or dissociative adsorption. The approach uses the spectral-grid method, in which the molecular wave function is represented by its values on a fixed grid of points in space. This wave function is evolved in time, scattered from the surface, and used to compute all properties of interest. The ro-vibrational part of the wave function is treated exactly, avoiding the usual rigid-rotor approximation. The rotationally inelastic diffraction of H{sub 2}, HD, and D{sub 2} from a metal surface is examined. It is found that small variations in the molecular bond length near the surface can lead to significant variations in the rotationally inelastic scattering probabilities. This is important since many metals interact chemically with H{sub 2}, and their scattering probabilities are often used to extract information about the gas-surface potential. Applications of the method to other problems are discussed.