Some reactions of Ar 2+ with atoms and molecules at 300 K

Abstract

The reactions of the ground ( 3p) and metastable ( 1S o) states of Ar 2+ with atoms (He, Ar and Xe) and molecules (H 2, N 2, O 2, CO 2 and CH 4) have been studied in the Selected Ion Flow Tube (SIFT) at 300 K. The Ar 2+ ions were generated in a low pressure ion source. Argon and helium were used separately as carrier gases since they reactively remove the 1S o and 3P states respectively, thus leaving only one Ar 2+ state in the flow tube. The rate coefficients for the reactions with atoms are generally smaller than those involving molecules, except for the reactions with Xe, which are rapid, presumably as a result of favourable energy resonances. Such resonances can often be achieved in the single charge transfer reactions of doubly-charged ions since the exoergicity of the reaction can be absorbed as the kinetic energy of repulsion of the product ions. The reactions with H 2 and CH 4 proceed by single charge transfer, the 1S o reactions resulting in a large degree of fragmentation of the molecular product ions. The reactions with N 2, O 2, and CO 2 are strikingly different in that double charge transfer in a single collision followed by dissociation into two singly-charged ions is the only observed reaction mechanism.