The electronic structure of hydroxyl molecules trapped in small neon clusters

The electronic structure of small NenOH clusters, with n = 6 or 12, is examined within the approximate Restricted Hartree–Fock framework. The purpose of these calculations is to examine the integrity and modifications of the trapped molecule OH within the host atom cluster, Nen, and to contribute to understanding molecules trapped in matrices. We have limited this study to small planar neon clusters and hence do not present a full three-dimensional picture of a molecule trapped in a microcrystal. The Ne6OH system is stable with respect to Ne6 and OH by ∼10 kcal/M and trapping of a hydroxyl into the cluster is exothermic. In a rough comparison between electronic factors and van der Waals contributions, it is claimed that the van der Waals contributions do not account for the most important aspects of the trapping in this small cluster. The ionization potentials of OH are all lowered when OH is trapped in this small cluster. An interpretative study based on electronic charge densities is presented. The integrity and modifications of the hydroxyl are examined by consideration of orbital, total, and certain difference densities for OH when free and trapped in the cluster. We find that there is apparently a small transfer of charge from the neon cluster to the hydroxyl molecule and the density maps show many features characteristic of normal bonding density maps, although at a much lower scale. The barrier to rotation in the plane is obtained and found to be very small consistent with finding for OH trapped in a neon matrix. We find there are no significant changes in the potential energy curve, E(R), for the hydroxyl molecule in the matrix as compared to the free molecule.