Effect of HNO3 and HCl on D2O Desorption Kinetics from Crystalline D2O Ice

Abstract

The presence of trace species may perturb H2O desorption kinetics from ice surfaces and alter the stability of atmospheric ice particles. To investigate the effects of atmospheric species on H2O desorption kinetics from crystalline ice, the D2O desorption kinetics from pure and HNO3- and HCl-dosed crystalline D2O ice multilayers on Ru(001) were investigated using isothermal laser-induced thermal desorption (LITD) measurements. The D2O desorption kinetics were studied for D2O ice film thicknesses of 25−200 BL (90−730 Å) and initial acid coverages of 0.5−3.0 BL for HNO3 and 0.3−5.0 BL for HCl. Arrhenius analysis of the D2O desorption rates from pure D2O crystalline ice at T = 150−171 K yielded a desorption activation energy of Ed = 13.7 ± 0.5 kcal/mol and a zero-order desorption preexponential of νo = (3.3 ± 0.7) × 1032 molecules/(cm2 s). The absolute D2O desorption rates were ∼3−5 times smaller for D2O ice films exposed to HNO3. The D2O desorption kinetics from HNO3-dosed ice were Ed = 11.3 ± 0.4 kcal/mol and νo = (5.0 ± 0.9) × 1028 molecules/(cm2 s). In contrast, the absolute D2O desorption rates were ∼2 times larger for D2O ice films exposed to HCl. The D2O desorption kinetics from HCl-dosed ice were Ed = 14.2 ± 0.6 kcal/mol and νo = (3.7 ± 0.8) × 1033 molecules/(cm2 s). The changes in the D2O isothermal desorption kinetics were independent of DNO3 and DCl coverages. The adsorbate-induced perturbations are believed to be associated with the formation of stable hydrate cages and reduced D2O mobility in HNO3-dosed ice and the creation of defects and enhanced D2O mobility in HCl-dosed ice. The effects of HNO3 and HCl on the D2O desorption kinetics indicate that the growth, stability, and lifetimes of atmospheric ice particles should be altered by the presence of adsorbates on the ice surface.