Abstract
AbstractThe real time kinetics of adsorption and desorption of HCl on ice have been studied in a very low pressure reactor (Knudsen cell). We used two complementary techniques, namely pulsed valve or transient supersaturation and steady state experiments. The kinetics of adsorption, following a first order rate law, has been found to depend on the number of HCl molecules in a pulse for transient supersaturation and on the HCl partial pressure or flow rate in steady state experiments. The uptake coefficient γ ranges from 0.34 to 0.22 in the temperature range 190 to 210 K for dry adsorption leading to a quasi‐liquid state of HCl on ice and from 0.31 to 0.13 for adsorption leading to a liquid solution of HCl. In both cases a negative temperature dependence for uptake of HCl on ice of −1.8±0.5 and −3.1±0.5 kcal/mol has been observed. In addition, the fraction of HCl that could be retrieved by desorption after dosage with HCl depended strongly on the thermodynamic state of the HCl/ice substrate as well as on the temperature and varied in the range from 10 to 80%. We determined the rate of irreversible surface‐to‐bulk loss, with a limiting rate of 1.0·1013 molecule s−1 cm−2 at 200 K. In addition, we studied the kinetics of adsorption of HBr and HI on ice resulting in γ values similar to HCl. However, ice in the range 190 to 210 K did not support any measurable vapor pressure of both HBr and HI after adsorption of up to several formal monolayers in contrast to HCl.
Published Version
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