Symmetry constraints in energy transfer between state-selected Ar*(3P2, 3P0) metastable atoms and ground state H atoms

Abstract

The excitation-transfer reaction in thermal energy collisions of state-selected metastable Ar*( 3 P 2 ) and Ar*( 3 P 0 ) atoms with ground state H atoms, giving excited H*( n = 2) atoms, has been studied with the stationary afterglow technique. The rate constant for the excitation of H atoms by Ar*( 3 P 2 ) has been found to be more than one order of magnitude larger than in excitation by Ar*( 3 P 0 ). This difference in the reactivity of two metastable species is explained to be a consequence of the attractive nature of the D( 2 II) and E( 2 Σ + ) potentials that develop from the Ar*( 3 P 2 )+H entrance channel and which give curve crossing with the B( 2 II) and C( 2 Σ + potentials, respectively, leading to the Ar+H*( n =2) exit channel, whereas only a repulsive 4 II (Ω= 1 2 ) potential develops from the Ar*( 3 P 0 +H entrance channel.