STRUCTURES IN THE LONG-RANGE POTENTIAL CURVES OF NA-2 .2. APPLICATION TO THE SEMICLASSICAL STUDY OF THE ENERGY POOLING PROCESS BETWEEN 2 EXCITED SODIUM ATOMS

Recent accurate calculations by Magnier et al have demonstrated that for some symmetries the long-range excited adiabatic potential curves of thc 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] --> Na[3s] + Na[5s, 4d, 4f] in the framework of a semiclassical multicrossing Landau-Zener model. All the pseudo-crossings of the adiabatic potential curves from thc Na[3s] + Na[4p] up to thc Na[3s] + Na[4f] dissociation limit have been considered. At thermal collision energy (T almost-equal-to 500 K) cross sections are in good agreement with available experimental data. At lower collision energy (T almost-equal-to 200 K), we show that a 1SIGMA(g)+ and a 3SIGMA(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.