Reactions of Ne2+, Ar2+, Kr2+and Xe2+with the rare gases at low energies

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Abstract
The rate coefficients and product ions for the reactions Ne2+, Ar2+, Kr2+ and Xe2+ ions with He, Ne, Ar, Kr and Xe have been determined in the Birmingham selected-ion flow tube (SIFT) at 300K, and the energy variation of several of these reactions has been studied in the Innsbruck drift tube (IDT). In the case of Xe2+, the reactions of the ground state (3P) and the metastable electronic states (1D2 and 1S0), were studied whereas for Ar2+ a study of only the 3P and 1S0 state reactions was possible. In the case of Ne2+ no state selection was achieved and for Kr2+ state selection was only achieved in the reaction with Ne. Single charge transfer was the only observed mechanism in all of the reactions except the Ne2+ reactions with Kr and Xe in which double charge transfer channels were also evident. The widely varying rate coefficients are interpreted in terms of a model involving the internuclear separation, Rx, at which the ion-induced dipole attractive and the Coulombic repulsive potential curves cross, and which indicates that a 'reaction window' exists for Rx between 2 and 6 AA. The drift tube data are totally consistent with the model and the increasing rate coefficients with increasing energy for the Kr2+(1D2)+Ne and Xe2+(3P)+Ar reactions clearly indicate an increasing efficiency for the production of the 2P1/2 states of Kr+ and Xe+ rather than the 2P3/2 states which are the favoured products at thermal energies.