Hydrogen Desorption from Polycrystalline Palladium

Abstract

The investigation of the internal energy distribution of molecules after the interaction with a surface by tunable laser spectroscopy has attracted much interest recently. While several research groups have studied the scattering of molecules from surfaces [1, 2], only a few experiments have been carried out on the desorption of molecules. A major difficulty arises from the fact that the measurement time during molecular desorption from a previously cold surface is relatively short, lasting only minutes. A complete rotational population distribution can thus only be obtained from several successive adsorption - desorption cycles. In this way Cavanagh and King investigated the desorption of NO from Ru(001) [3]. This experimental constraint has been removed recently by studying the desorption of hydrogen which can permeate through metal, allowing thus a continuous desorption experiment at controlled surface temperature [4, 5]. In addition to these experimental advantages detailed information is available about the recombinative desorption of hydrogen from metal surfaces. Angular distributions sharply peaked in the forward direction, proportional to cosnθ with 3 ≤ n ≤ 10 have been observed [6, 7]. Also fast velocity distributions with mein kinetic energy up to four times the surface thermal energy have been measured [7, 8]. These deviations from Knudsens cosine law and from the Maxwellian kinetic energy distribution suggest dynamical constraints to this process, which should also be reflected in the population distribution of the molecular quantum states. In this contribution we report results on the recombinative desorption of H2[5] and D2 molecules from a polycrystalline palladium surface.KeywordsRotational EnergyHydrogen DesorptionInternal Energy DistributionExperimental AdvantageSuccessive AdsorptionThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.