Diffusion kinetics of HC1 hydrates in ice measured using infrared laser resonant desorption depth-profiling

The diffusion kinetics of HCl hydrates in ice were measured using a new infrared laser resonant desorption (LRD) depth-profiling technique. This LRD technique permits quantitative depth-profiling and real lime diffusion measurements in ice with submicron spatial resolution and high sensitivity. The diffusion coefficients of HCl hydrates ranged from D = 2.0(+/-0.6) x 10(-13) cm(2)/s at T = 169.0 K to D = 1.1(+/-0.2) x 10(-10) cm(2)/s at T = 194.9 K. Arrhenius analysis of the diffusion rates yielded a diffusion activation energy of E-A = 15.3 +/- 1.0 kcal/mol and a diffusion preexponential of D-o = 1.5 x 10(7 +/-0.2) cm(2)/s, The diffusion coefficients were independent of the total diffusion time and the initial HCl exposure conditions used to prepare the HCl hydrates. The HCl diffusion rates were comparable to H2O diffusion rates in pure ice and HCl-dosed ice multilayers. This similarity between the HCl and H2O diffusion rates suggests that HCl hydrate diffusion in ice may be dependent on the diffusion of H2O vacancies.