AVS 45th International Symposium
    Surface Science Division Friday Sessions
       Session SS2-FrM

Paper SS2-FrM4
Origin of Non-Zero-Order H@sub2@O Desorption Kinetics from Crystalline Ice Multilayers on Ru(001)

Friday, November 6, 1998, 9:20 am, Room 309

Session: Water and Ice Interfaces
Presenter: F.E. Livingston, University of Colorado, Boulder
Authors: F.E. Livingston, University of Colorado, Boulder
J.A. Smith, University of Colorado, Boulder
S.M. George, University of Colorado, Boulder
Correspondent: Click to Email
Recent studies have reported non-zero-order kinetics for H@sub2@O desorption from crystalline ice multilayers on Ru(001). To understand the origin of the non-zero-order kinetics, D@sub2@O desorption from ultrathin crystalline D@sub2@O ice multilayers on Ru(001) was measured using a combination of laser-induced thermal desorption (LITD) spatial probing and isothermal desorption flux analysis. The ice multilayers were grown on Ru(001) using either backfill D@sub2@O vapor deposition or multichannel capillary array dosing methods. The ice multilayers grown via backfill vapor deposition were smooth and highly uniform. The LITD and isothermal desorption flux studies demonstrated that D@sub2@O desorption from these uniform ice multilayers exactly followed zero-order kinetics. Slight deviations from zero-order desorption kinetics were observed only at low D@sub2@O coverages of @<=@5 BL D@sub2@O. In contrast, the ice films prepared using capillary array dosing were spatially non-uniform and exhibited a decreasing multilayer coverage versus distance from the center of the substrate. This initial non-uniform D@sub2@O coverage distribution had a dramatic impact on the isothermal desorption flux measurements and produced non-zero-order desorption kinetics. The deviations from zero-order kinetics were directly related to changes in the ice film surface area as the non-uniform initial multilayer coverage is completely desorbed at various positions on the Ru(001) substrate at different times. The previous reports of non-zero-order kinetics on Ru(001) are assigned to a non-uniform initial D@sub2@O multilayer coverage distribution.