Depopulation of low-Rydberg Na atom in collisions with rare gases: A molecular-state treatment

Total quenching of the low-Rydberg state of Na in collision with thermal Ne and Ar was investigated, for the first time, employing a molecular approac h in the impact parameter formalism. A large basis set of Slater-type orbit als was used to calculate the molecular structure of the transient quasimol ecule formed during the collision; pseudopotentials were used to incorporat e the effective binding of the distant electron. A 14-channel calculation w as carried out to evaluate the total depopulation cross sections for Na(9s) colliding with the ground-state Ne and Ar atoms in the thermal-energy regi on. The two colliding pairs not only differ from each other, but also show wide variations from the previously studied Na-He pair, in terms of details of the collision dynamics. In the case of the Na-Ar system, a unique featu re that leads to appreciably larger quenching cross sections shows qualitat ive agreement with the measurement. A comparative study of three (He/Ne/Ar- Na) colliding pairs reveals that the simplified approach like the free-elec tron model or the impulse approximation fails to provide details of such st ate-changing reactions. (C) 1999 John Wiley & Sons, Inc. Int J Quant Chem 7 3: 307-316, 1999.