State selected ion–molecule reactions by a TESICO technique. II. Separation of the reactant spin–orbit states in the reaction Ar+(2P3/2, 2P1/2)+H2(D2)→ArH+(ArD+)+H(D)

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Abstract
Cross sections for the atomic rearrangement reaction Ar++H2(D2)→ArH+(ArD+)+H(D) [Reaction (1)] and the charge transfer reaction Ar++H2(D2)→Ar+H+2(D+2) [Reaction (2)] have been determined for each of the Ar+ spin–orbit states (2P3/2 and 2P1/2) separately in the collision energy range from 0.05 to 0.5 eV (c.m.), utilizing the threshold electron–secondary ion coincidence (TESICO) technique which we developed recently. It has been found that the cross sections of Reaction (1) are larger for the 2P1/2 excited state than for the 2P3/2 ground state by a factor of 1.5 (with H2) and 1.3 (with D2), regardless of the collision energy in the range studied. The cross sections for both the H2 and D2 reactions show an approximately E−1/2.5 collision energy dependence which is somewhat milder than that expected from the simple Langevin theory. The cross sections of Reaction (2) have been found to be about seven times larger for the 2P1/2 state than for the 2P3/2 state with H2, whereas these are almost the same for both states with D2. The charge transfer cross sections are almost independent of the collision energy in the same energy range as above. A simple reaction model has been developed and a calculation of cross sections has been performed based on it, with a result which satisfactorily explains the essential features of the experimental results.