New determinations of quantitative forward rate constants for reactions of titanium monomer cation with C 2 H 6 , C 3 H 8 , H 2 O, NH 3 , and O 2 are accomplished using a high-pressure (multicollision) flow tube reactor. These experiments were prompted by our observation of conflicting reports in the literature. The reaction rates we consider have been determined previously by both single-collision and multicollision methods, with some systems having generated notably contrasting results. An effort is made to reconcile the difference in values by explicitly addressing possible potential sources of error which have been suggested in earlier publications as the most likely reasons for the discrepancies. A "titration" technique is employed which allows controlled collisional quenching of excited state titanium cations with nitrogen gas such that excited state ion effects can be selectively observed and subsequently eliminated. No evidence is found to cast doubt upon the validity of multicollision methods for the determination of thermal energy rate constants.

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Results of studies of the uptake of HCl by the deuterated analogue of protonated water clusters are reported. The successive uptake of nHCl n = 1−4 is observed, n = 2−4 appearing in a stepwise manner with a ratio of 6:1 D2O/HCl for the bimolecular reaction products. This primary uptake scheme is observed over a range of pressures (0.24−0.46 Torr) and temperatures (130−170 K). However, for increased flows of HCl, enhanced uptake is observed at a lower ratio of D2O/HCl, a trend that is effected by an increased buffer gas pressure. Two distinctly dominant mechanisms of HCl uptake are operative:  the bimolecular uptake of HCl in a 6:1 ratio with water and a subsequent association mechanism of HCl binding to water in a 3:1 ratio. The atmospheric implications are discussed along with a proposed molecular activation by surface coordination (MASC) model for HCl uptake and subsequent reactivity on polar stratospheric clouds.

The results of a detailed study of the uptake of HCl by the deuterated analogue of protonated water clusters are reported. The primary uptake of HCl is found to occur by bimolecular reaction whereupon studies at a variety of pressures indicate that no termolecular process is involved. Interestingly, varied temperature studies indicate an inverse temperature dependence on the bimolecular rate constants. The discussion is partitioned between efficiency considerations of the experimentally determined kinetics and atmospheric interpretations of HCl uptake, the latter involving comparisons to mass accommodation coefficients measured using ice films as polar stratospheric cloud mimics.

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