Ab initio calculations of energy transfer and non-additivity in the He-Ne laser system

Ab initio calculations were performed for several suggested mechanisms of e nergy transfer between helium metastable particles and neon. Optimized geom etries and excited-state energies were calculated for neon excited-state co mplexes and the convergence properties of the non-additive contributions to the interaction energies were examined. The most probable excitation-trans fer mechanism was found to be He-2(m) (a(3)Sigma(u)(+)) + Ne --> (He2Ne)(r) * --> Ne(2p(5)3s) + 2. He based on an energy difference of 0.0674 eV betwee n the triplet excited state of He-2(m) and the singlet excited state of (He NeHe)(r)*. No theoretical evidence was found for the production of neon sin glet excited-state complexes other than 20.0858 to 20.4875 eV by the consid ered two-, three- and four-body models of energy transfer processes. The en ergy curves of the reactions involving the excited-state complexes (HeNeHe) (r)* and (HeNe)(r)* are provided and compared with the previously reported experimental results on the reaction He-2(m) (a(3)Sigma(u)(+)) +Ne --> (He2 Ne)(r)* --> Ne(2p(5)3s) +2 He. The relation between the probability of ener gy transfer and laser activity is discussed. The non-additive contribution to the total interaction energy of the nominated (HeNeHe)(r)* intermediate complex was found to be negligible, pointing to the possibility of construc ting model potentials and simulation of larger systems.