Isothermal Desorption Kinetics of Crystalline H2O, H218O, and D2O Ice Multilayers

Abstract

The isothermal desorption rates of crystalline H2O, H218O, and D2O ice multilayers were measured over a temperature range from 175 to 190 K. The desorption rates were measured with optical interferometry using ice multilayers grown epitaxially on a Ru(001) surface in an ultrahigh vacuum chamber. The Arrhenius parameters for the desorption of H2O and H218O were identical within experimental error. For H2O, the preexponential was ν = 1032.6±0.3 cm-2 s-1 and the activation energy was E = 13.9 ± 0.2 kcal mol-1. For H218O, the preexponential was ν18 = 1032.4±0.3 cm-2 s-1 and the activation energy was E18 = 13.8 ± 0.2 kcal mol-1. Despite the near equivalence in the Arrhenius parameters, H218O desorbed at a rate that was slower by ∼9% throughout the range of temperatures. In contrast, the desorption rate of D2O was slower by 49−62% compared with H2O over the measured temperature range. The Arrhenius parameters for the desorption of D2O were νD = 1033.4±0.5 cm-2 s-1 and ED= 14.8 ± 0.4 kcal mol-1. A transition sta...