Variable-temperature selected ion flow tube studies of the reactions of Ar+, Ar+2 and ArH+n (n = 1-3) ions wi H2, HD and D2 at 300 K and 80 K

doi:10.1016/0168-1176(90)85017-V

International Journal of Mass Spectrometry and Ion Processes

Volume 98, Issue 2, 1 August 1990, Pages 179-190

International Journa...

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Abstract

The reactions of Ar⁺, Ar⁺₂, ArH⁺ (ArD⁺), ArH⁺₂ (ArHD⁺, ArD⁺₂) and ArH⁺₃ with H₂, HD and D₂ have been studied at 300 K and 80 K using our variable-temperature selected ion flow tube (VT SIFT). The Ar⁺ reactions proceed via parallel H-atom abstraction (major channel) and charge transfer, and the rate coefficients, k, are about 0.55 times the collisional rate coefficients, k_c, at both temperatures for the three reactions. The ArH⁺ (ArD⁺) reactions proceed via proton (deuteron) transfer, and the k values are about 0.6 · k_c at 300 K and about 0.75 · k_c at 80 K. The Ar⁺₂ reactions proceed via two parallel channels, for example, the H₂ reaction produces ArH⁺ (atom abstraction) and ArH⁺₂ (Ar atom/H₂ molecule switching); the analogous reactions occur with HD and D₂. Whilst the atom abstraction channel is favoured at 300 K (in the ratio of about 70:30) the two channels are comparable at 80K for all three reactions. The overall K value for these reactions is about 0.3·k_c at 300 K increasing to about (0.5–0.6)·k_c at 80 K; in effect, the switching reactions are significantly enhanced at the low temperature. The ArH⁺₂ reaction with H₂ produces ArH⁺₃; similarly ArH₂D⁺, ArHD⁺₂ and ArD⁺₃ are produced in the other reactions. The k values are about 0.7·k_c at both temperatures. From these studies, the dissociation energy of Ar·H⁺₂ (to Ar + H⁺₂) is shown to be ⩾ 1.04 eV and that of ArH⁺₃ (to Ar + H⁺₃) is shown to be within the range 0.29–0.36 eV.

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International Journal of Mass Spectrometry and Ion Processes

Abstract

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