The uptake of HI and HBr on ice

Abstract

A low pressure flow system equipped with mass spectrometric detection has been employed to study the heterogeneous reactivity of HX (where X=I or Br) on solid ice; HX(g)+H₂O(s)→products. HX uptake coefficients were measured on ice films with HX concentrations in the range (1–30)×10¹² molecule cm^-3 and over the temperature range 200–233 K. The steady state reactive uptake coefficient for HI was found to be constant at T>212 K, γ=0.02±0.004 and for HBr γ=0.03±0.005, independent of concentrations used. Below 212 K a large increase in the rate of uptake of HX on ice was observed with γ0.1 for both HI and HBr. The apparent increase in the reactivity of ice was attributed to an increase in the surface area due to the increased porosity of ice at lower temperatures.