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The positive ion¬negative ion reactions of Kr^+(^P_) The positive ion-negative ion reactions of Kr^+(2P1/2,3/2) with C_6F_5Cl^-, and Xe+(2P1/2,3/2) with SF_6-, C_6F_6^-, and C_6F_5Cl^- have been spectroscopically studied in the He flowing afterglow. KrCl* excimer and excited Kr* atoms were produced in the Kr^+/C_6F_5Cl^- reaction, whereas XeF*, Xe*, and XeCl* and Xe* were formed in the Xe^+/SF_6-, Xe^+/C_6F_6-, and Xe^+/C_6F_5Cl^- reactions, respectively. The branching ratios between recombination and neutralization reactions leading to RgX* (Rg = Kr, Xe, X = F, Cl) excimers and excited Rg* atoms, respectively, were found to be 0.69:0.31 for the Kr^+/C_6F_5Cl^- reaction and 1.00:0.00, 0.00:1.00, and 0.89:0.11, for the Xe^+/SF_6^-, Xe^+/C_6F_6^-, and Xe^+/C_6F_5Cl^- reactions. These results suggested that the branching ratio between recombination and neutralization reactions depends strongly on the negative ion. It was concluded that dissociation energies of target anions leading to X^- and electron affinities of target molecules play a significant role in the ion-ion recombination and neutralization reactions of Rg^+ with SF_6^-, C_6F_6^-, and C_6F_5Cl^-.

RgCl(B,C,D) excimers were produced for Rg = Ar, Kr, and Xe by the positive ion-negative ion recombination reactions of Rg^+(^2P_) with C_6F_5Cl^- in the flowing afterglow. Spin-orbit state selectivity of RgCl(B,C,D) excimers by the Rg^+(^2P_) and Rg^+(^2P_) components was examined by using appropriate filter gases of one spin-orbit component. The RgCl(B,D) ratio was determined to be 0.35:0.65, 0.05:0.95, and 0.24:0.76 in the Ag^+(^2P_), Kr^+(^2P_), and Xe^+(^2P_) reactions, whereas the RgCl(B,C) ratio was estimated to be 0.74:0.26, 0.71:0.29, and 0.70:0.30 in the Ag^+(^2P_), Kr^+(^2P_), and Xe^+(^2P_) reactions, respectively. The Rg^+(^2P_) reactions had a high propensity to give RgCl(D) plus a lesser amount of RgCl(B), whereas the Rg^+(^2P_) reactions gave only RgCl(B,C). These results show that Rg^+(^2P_) + Cl^- and Rg+(^2P_) + Cl- characters are conserved well for the formation of RgCl* in the ion-ion recombination reactions between Rg^+(^2P_) and C_6F_5Cl-. Higher conservation of Rg^+(^2P_) character in the Rg^+(^2P_)/C_6F_5Cl- reactions than that in the Rg(^3P_0)/halides reactions is discussed by using correlation diagram between entrance and exit product channels.

The positive ion–negative ion reactions of Kr^+ and Xe^+ with C_6F_5Br^- and C_6F_5CF_3^- have been spectroscopically studied in the He flowing afterglow. The branching ratios of recombination and neutralization reactions leading to RgX* excimers and excited Rg* atoms (Rg = Kr, Xe, X = Br, F), respectively, were determined to be 0.14:0.86 and 1.00:0.00 for the Kr^+/C_6F_5Br^- and Xe+/C_6F_5Br^- reactions and 0.00:1.00 for both the Kr^+/C_6F_5CF_3^- and Xe^+/C_6F_5CF_3^- reactions. It was concluded that electron affinities of target molecules and dissociation energies of C_6F_5X^- leading to X^- play a significant role in determining the branching ratio of ion–ion recombination and neutralization reactions.

Ion-molecule reactions of Ar_2^+, N_3^+, and N_4^+ cluster ions with CH_4, C_2H_2, C_2H_4, and C_2H_6 have been studied by using a thermal ion-beam apparatus. Rate constants were determined and compared with those obtained from Langevin theory. Rate constants of the Ar_2^+ + C_2H_2, Ar_2^+ + C_2H_4, and N_3+ + C_2H_6 reactions, which have not been measured, were determined to be 1.4, 8.1, and 3.6 × 10^ cm3 s^-1, respectively. These values correspond to 14%, 74%, and 28% of calculated rate constants from Langevin theory, respectively.