Charge-transfer reactions: absolute cross-sections measured by total charge collection

Abstract

The N 2 +/N 2, Ar +/Ar, Ar +/N 2- and N 2 +/Ar charge-transfer reactions have been investigated by passing a beam of the reactant ions through a zone containing the reactant gas. The absolute cross-sections have been measured by a total charge collection method, and the results obtained are of the same order as those reported by independent workers. The apparatus also permits mass analysis of the reaction components; this allows their purity to be assessed, and also is essential for studies of dissociative charge-transfer reactions. The variation of the cross-sections with translational energy has been investigated over the range 100–2000 eV, and the results indicate that in each system a number of parallel reactions are participating. Probable energy states of the reaction components have been postulated on the basis of the near-adiabatic hypothesis. The interpretations of the four systems are self-consistent and involve the following basic processes: (i) ionization of N 2 produces N 2 + in the v = 1 vibrational level, (ii) recombination of N 2 + ( v = 1) with an electron produces both N 2 ( v = 0) and N 2 ( v = 2) in the ground electronic state, (iii) ionization of Ar produces Ar + in the 2 P 3 2 and 2 P 1 2 states, and a further autoionization process occurs, and (iv) recombination of Ar + ( 2 P 3 2 ) and Ar +( 2 P 1 2 ) with electrons occur, and also of an Ar + species possessing an energy corresponding to its autoionization level.