Structures in the long-range potential curves of Na₂. II. Application to the semiclassical study of the energy pooling process between two excited sodium atoms

Abstract

Recent accurate calculations by Magnier et al. (1994) have demonstrated that for some symmetries the long-range excited adiabatic potential curves of the Na2 molecule display many avoided crossings, some of them being due to competition between ionic and covalent dissociation. We have used those molecular data to estimate cross sections for the energy pooling reaction: Na(3p)+Na(3p) to Na(3s)+Na(5s, 4d, 4f) in the framework of a semiclassical multicrossing Landau-Zener model. All the pseudocrossings of the adiabatic potential curves from the Na(3s)+Na(4p) up to the Na(3s)+Na(4f) dissociation limit have been considered. At thermal collision energy (T approximately=500 K) cross sections are in good agreement with available experimental data. At lower collision energy (T approximately=200 K), we show that a 1 Sigma g+ and a 3 Sigma u+ channel correlated to Na(3s)+Na(5s) dissociation limit become dominant. This illustrates the crucial role of long range crossings in the dynamics of collisions between excited sodium atoms at very low energies.