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

Recent accurate calculations by Magnier et al have demonstrated that f or some symmetries the long-range excited adiabatic potential curves o f thc Na2 molecule display many avoided crossings, some of them being due to competition between ionic and covalent dissociation. We have us ed those molecular data to estimate cross sections for the energy pool ing reaction: Na[3p] + Na[3p] --> Na[3s] + Na[5s, 4d, 4f] in the frame work of a semiclassical multicrossing Landau-Zener model. All the pseu do-crossings of the adiabatic potential curves from thc Na[3s] + Na[4p ] up to thc Na[3s] + Na[4f] dissociation limit have been considered. A t thermal collision energy (T almost-equal-to 500 K) cross sections ar e in good agreement with available experimental data. At lower collisi on energy (T almost-equal-to 200 K), we show that a 1SIGMA(g)+ and a 3 SIGMA(u)+ channel correlated to Na[3s] +Na[5s] dissociation limit beco me dominant. This illustrates the crucial role of long range crossings in the dynamics of collisions between excited sodium atoms at very lo w energies.