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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

1990; Elsevier BV; Volume: 98; Issue: 2 Linguagem: Inglês

10.1016/0168-1176(90)85017-v

1873-2801

D. K. Bedford, David Smith,

Quantum, superfluid, helium dynamics

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, kc, at both temperatures for the three reactions. The ArH+ (ArD+) reactions proceed via proton (deuteron) transfer, and the k values are about 0.6 · kc at 300 K and about 0.75 · kc 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·kc at 300 K increasing to about (0.5–0.6)·kc 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·kc 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.