Ab initio configuration-interaction studies of the ground state potential energy and hyperfine coupling constants of ³⁵Cl^-₂

Abstract

Potential energy and spectroscopic constants for the X ²Σ_u ⁺ ground state of Cl^- ₂, were calculated by configuration-interaction (CI) methods, using large basis sets with polarization and diffuse functions. From these CI wavefunctions, the isotropic (a _iso) and dipolar (A _dip) components of the hyperfine coupling constant were obtained. The effects of various s, p basis sets, polarization and diffuse functions, as well as the influence of reference configurations and configuration selection thresholds were investigated. The best values obtained are 35·31 G for a _iso and 29·44 G for A _dip, to be compared with experimental values of 37 ± 1 G and 32 ± 1 G, respectively. It is shown that the contributions to a _iso of the K and L shells are opposite in sign, differing by about 4 G. Upon vibrational averaging, both a _iso and A _dip move towards smaller values as v increases. An adiabatic electron affinity of 2·46 eV was obtained for Cl₂, and a vertical electron detachment energy of 3·71 eV for Cl^- ₂.