Potential energy surfaces for alkali plus noble gas pairs: a systematic comparison

Abstract

Optically Pumped Alkali Lasers (OPAL) involve interactions of alkali atoms with a buffer gas typically consisting of a noble gas together with C 2 H 4 . Line broadening mechanisms are of particular interest because they can be used to match a broad optical pumping source with relatively narrow alkali absorption spectra. To better understand the line broadening processes at work in OPAL systems we focus on the noble gas collisional partners. A matrix of potential energy surfaces (PES) has been generated at the multi-configurational self consistent field (MCSCF) level for M + Ng, where M=Li, Na, K, Rb, Cs and Ng=He, Ne, Ar. The PES include the X 2 Σ ground state surface and the A 2 II, B 2 Σ excited state surfaces. In addition to the MCSCF surfaces, PES for Li+He have been calculated at the multi-reference singles and doubles configuration interaction (MRSDCI) level with spin-orbit splitting effects included. These surfaces provide a way to check the qualitative applicability of the MCSCF calculations. They also exhibit the avoided crossing between the B2Σ and A 2 II 1/2 surfaces that is partially responsible for collision induced relaxation from the 2 P 3/2 to the 2 P 1/2 atomic levels.