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.
Potential reaction mechanisms of D ϩ (D2O)n (n ϭ 4Ϫ30) with chlorine nitrate (ClONO2) have been investigated using a fast flow reactor operated under thermal conditions. Chemical reactions are not observed to occur between D ϩ (D 2 O) n and chlorine nitrate. Instead, through studies employing the heavy isotope of hydrogen, we found that the nitric acid observed in the product ion spectrum arises from a nitric acid impurity that is usually present to some degree in the methods employed to synthesize ClONO2 reactant gas. The results from this study serve to explain other conflicting reaction mechanisms reported in the literature, and which have been discussed in the context of atmospheric chemistry.
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