THEORETICAL CHARACTERIZATION OF THE LOW-LYING EXCITED-STATES OF THE CUCL MOLECULE

The character of the low-lying excited states of diatomic CuCl is stud ied primarily by means of the complete active space self-consistent fi eld (CASSCF), method and a second order perturbation approach with the CASSCF wave function as reference state [complete active space pertur bation theory to second order (CASPT2)]. Far comparison, the lower lev els of the spectra of the Cu+ ion are also analyzed. A first order tre atment of the scalar relativistic effects, the mass-velocity and Darwi n terms, is included in the calculations. The importance of spin-orbit interactions is investigated by comparing our nonrelativistic valence shell CI (VCI) and relativistic results obtained with our four-compon ent program suite MOLFDIR. The six lowest excited states of the CuCl m olecule, which are related to the Cu+(3d(9)4s(1))Cl-(3s(2)3p(6)) ionic configuration, are assigned. The assignments agree with earlier theor etical work. Where they can be compared, the calculated spectroscopic constants are in good agreement with the experimental data. (C) 1997 A merican Institute of Physics.