Ab initio configuration-interaction studies of the ground state potential energy and hyperfine coupling constants of $^{35}$Cl$_2^-$

Abstract

Potential energy and spectroscopic constants for the X$^2 \sum^+ _\mu$ ground state of a;, were calculated by configuration-interaction (Cl) 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 29·440 for A$_{dip}$• tobe compared with experimental values of 37 ± 1 G and 32 ± 1 G, respectively. It is shown that the contributions to a1so 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 2·46eV was obtained for CL$_2$ , and a vertical electron detachment energy of 3·71 eV for Cl;