CEPA calculations on open-shell molecules

Abstract

Ab initio calculations at SCF and CEPA levels using large Gaussian basis sets have been performed for the two lowest electronic states,X2 Σ+ andA2 Π, of HeAr+. Spin-orbit coupling (SOC) effects have been added using a semiempirical treatment. The resulting potential curves for the three statesX,A1, andA2 have been used to evaluate molecular constants such as vibrational intervals ΔG(v + 1/2) and rotational constantsB v as well as — by means of a Dunham expansion — equilibrium constants such asR e , ω e ,B e etc. Comparison with the experimental data from UV emission spectroscopy shows that the calculated potential curves are slightly too shallow and have too large equilibrium distances:D e = 242 cm−1 andR e = 2.66 A compared to the experimental values of 262 cm−1 and 2.585 A, respectively, for theX2Σ+ ground state. However, the ab initio calculations yield more bound vibrational levels than observed experimentally and allow for a more complete Dunham analysis, in particular for theA2 state. The experimental value of 154 cm−1 for the dissociation energyD e of this state is certainly too low; our best estimate is 180±5 cm−1. For theA1 state our calculations are predictions since this state has not yet been observed experimentally.