AVS 46th International Symposium
    Surface Science Division Monday Sessions
       Session SS3-MoM

Paper SS3-MoM9
Cation Trapping Effects on HCl Diffusion in Ice Measured Using a New Laser Resonant Desorption Depth-Profiling Technique

Monday, October 25, 1999, 11:00 am, Room 612

Session: Water-Surface Interactions
Presenter: F.E. Livingston, University of Colorado, Boulder
Authors: F.E. Livingston, University of Colorado, Boulder
S.M. George, University of Colorado, Boulder
Correspondent: Click to Email
HCl diffusion in ice is important for an understanding of heterogeneous atmospheric chemistry on ice particles and may influence the interpretation of ice core data. The diffusion of alkali metals in ice is also relevant for the evaluation of ice core samples and alkali cations may interact strongly with coadsorbates in ice. Novel laser resonant desorption depth-profiling techniques were used to measure HCl and Na diffusion in ice. The diffusion was monitored using a Q-switched Er:YAG laser to depth-profile the ice multilayer. The Er:YAG laser emits infrared light at 2.94 microns. This light can be resonantly absorbed by the O-H stretching vibration of H@sub2@O and thermalized to induce resonant desorption. HCl diffusion was monitored in ice multilayers containing a thin HCl interlayer. The HCl spatial coverages at various diffusion times and temperatures were used to extract the diffusion coefficients. The measured HCl diffusion coefficients ranged from D=(3.8±2.8)x10@super-13@ cm@super2@/s at T=169 K to D=(2.0±1.5)x10@super-10@ cm@super2@/s at T=197 K. Arrhenius analysis yielded diffusion kinetic parameters of E=14.6±1.6 kcal/mol and D@subo@=(2.9±2.0)x10@super6@ cm@super2@/s. Na was also observed to diffuse in the ice multilayers. In addition, coadsorbed Na decreased the HCl diffusion rate by a factor of ~5-85 for Na/Cl ratios ranging from 0.05-0.5. The Na-induced decrease in the HCl diffusion rate may be attributed to cation trapping manifested by NaCl formation in the ice.