Pseudopotential and multiple scattering xα calculations of nuclear quadrupole coupling constants and other properties of diatomic halogen molecules and their monoanions and monocations

Abstract

An SCF molecular orbital Pseudopotential method has been used to calculate the equilibrium bond lengths, dissociation energies and harmonic force constants for the homonuclear diatomic halogen molecules and their monoanions and monocations (X 2, X 2 −, and X 2 +, X = Br, I). The results were used to calculate the vertical and adiabatic ionization energies and electron affinities of Br 2 and I 2. These calculations were carried out using a modified version of Pople's GAUSSIAN 82 program in which the core electrons on Br and I are described by quasirelativistic core pseudopotentials. The SCF MS-Xα method has been used to calculate the nuclear quadrupole coupling constants for X 2, X 2 − and Xa 2 + for X = Cl, Br, I using the equilibrium intemuclear distances obtained from the Gaussian SCF calculations. For X 2 and X 2 −, agreement between the calculated and observed coupling constants is reasonable (within 10% for X 2 and 20% for X 2 −). In agreement with experiment, the ratio e 2 qQ(X 2 −)/e 2qQ(X 2) is less than 0.5, the value predicted by a simple Townes and Dailey analysis, and possible reasons for this difference are discussed.