Controlling the Relative Orientation of Reactants with Intermolecular Forces: Intermolecular State-Dependent Structure in Prereactive H2−OH Complexes

Abstract

A theoretical study has been carried out to examine the orientation distribution functions of the OH and H2 diatoms in various intermolecular states of the prereactive H2−OH complex. Multidimensional quantum calculations have been conducted on a high-quality ab initio intermolecular potential energy surface to obtain the energies and body-fixed wave functions for the rovibrational states of H2−OH. These calculations show that the H2 and OH diatoms undergo nearly free internal rotation within the complex. However, the angular anisotropy of the intermolecular potential orients the OH and aligns the ortho-H2 internal rotational motions within the complex. The relative orientation of the reactants is found to be well-defined and strongly intermolecular-state-dependent. Thus, by accessing different intermolecular states, the relative orientations of the reactants can be systematically manipulated. The degree of body-fixed orientation of OH in some bound states of H2−OH, including the ground state of ortho-H2−OH, approaches the highest degree of space-fixed orientation that has been achieved in hexapole orientation studies of OH. The experimental implications of the results are discussed.