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.