A joint vibro-electronic mechanism in the dissociation of molecular hydrogen in nonequilibrium plasmas

Abstract

A new mechanism Of H 2 dissociation in electrical discharges (10 11 ⩽ n e ⩽ 10 12 cm −3, 2.10 −16 ⩽ E/ N ⩽ 3.10 −16 V cm 2, 300 ⩽ T g ⩽ 1000 K, 3 ⩽ p ⩽ 30 torr) is presented and discussed. In this mechanism, called joint vibro-electronic mechanism (JVE), the electrons of the discharge create a strong vibrational disequilibrium with respect to the gas temperature ( T g) and promote electronic transitions from all vibrational levels of 1Σ g H 2 state to the repulsive 3Σ u one. Moreover the V-V (vibration-vibration) and V-T (vibration-translation) energy exchanges are considered for building up the vibrational distribution of 1Σ g state. A complete set of e - D cross sections (e + H 2( 1Σ g,ν) → e + H 2 ( 3Σ u) → + 2H, ν = 0,14) is calculated by using an extension of the semiclassical Gryzinski theory in combination with the Franck-Condon principle. Dissociation rates calculated according to JVE are larger either than those obtained by the pure vibrational mechanism (PVM) discussed in our previous work or than those from the direct electronic impact mechanism (DEM) from the ground vibrational level. The behaviour of JVE rates as a function of gas temperature ( T g), of E/ N, of electron density ( n e) and of pressure is then reported. The results show strong differences as compared, with the corresponding values obtained, with PVM. Finally the influence of the atoms as well as their recombination on the dissociation rates is discussed. The results have been obtained by solving a system of vibrational master equations.