The kinetics of adsorption and abstraction for the system H (D) on Al(100) has been investigated using an efficient atomic beam source, thermal desorption spectroscope and multiplexed mass spectrometry. Emphasis was put on the quantitative determination of the reaction parameters. The initial sticking coefficient for atomic hydrogen and atomic deuterium is 0.6; the saturation coverage is 1.6monolayers. On the D(H) saturated surface, abstraction takes place at a surface temperature of 150K due to impinging H (D) atoms (H+D→HD) with an abstraction coefficient of 0.4 D/H. No significant isotope effect can be observed. The abstraction process cannot be described by a direct Eley–Rideal mechanism, but rather by a hot-precursor mechanism. In addition to abstraction, about 10% of the adsorbed species are removed from the surface by a collision-induced associative desorption process.

The interaction of atomic hydrogen with clean and deuterium precovered Ni(110) surfaces at 150 K has been investigated using thermal desorption mass spectrometry. The initial sticking coefficient of atomic hydrogen is 0.9 +/- 0.1. Above saturation at 1.5 monolayers for dissociative H-2 adsorption, atomic hydrogen absorption leads to the occupation of subsurface sites with a penetration probability of 1 x 10(-2). Impingement of atomic hydrogen on a deuterium covered Ni(110) surface leads to deuterium abstraction via HD production with a removal coefficient of 0.26 HD molecules per H-atom (Eley-Rideal mechanism). In addition, removal of deuterium by associative D-2 desorption has been observed at T-s = 150 K, with a removal coefficient of 0.04 D-2 molecules per H-atom (collision induced recombinative Langmuir-Hinshelwood desorption). Interaction of atomic deuterium with a hydrogen covered surface yields an HD removal coefficient of 0.38 HD molecules and an H-2 removal coefficient of 0.06 H-2 molecules per D-atom.

Using the REMPI technique we have studied the internal state distribution of deuterium molecules produced by the interaction of atomic deuterium with chemisorbed deuterium on Ni(110) at 180 K. We observed molecules in vibrational states up to v=3 with a mean vibrational energy of 220 meV. The mean rotational energies of the molecules in the vibrational states v=0 to 3 are 185 meV, 133 meV. 75 meV and 37 meV, respectively. The overall mean rotational energy amounts to 150 meV, again far in excess of the mean rotational energy of molecules accommodated to the surface. The data are consistent with direct interactions of the impinging particles with the adsorbed particles (Eley-Rideal reaction and collision induced desorption), for which it is assumed that a considerable amount of the potential and kinetic energy of the impinging atoms is channeled into translational and internal energy of the reaction products.

Rotational and vibrational state distribution for H2, HD and D2 desorbing from clean and sulfur covered Ni(110) surfaces have been measured using resonantly enhanced multiphoton ionization (REMPI). For the clean surface the mean rotational energy of desorbing H2 and D2 is slightly smaller than kTs, with the lowest value of 0.75 kTs for HD. On the sulfur-covered surface a nearly thermalized rotational state distribution is observed for all three isotopes. The population of the first excited vibrational state is enhanced by a factor of two for H2 and D2 desorbing from the clean surface, compared with a Boltzmann distribution. With increasing sulfur coverage the population P(ν1) increases up to a sixfold overpopulation at Θs=0.5 ML. No orientational effects with respect to helicopter or cartwheel modes in the desorption flux of hydrogen could be observed.

Using nozzle beams we have determined the adsorption dynamics of H-2/W. On the rough (111) and (100) surfaces hydrogen adsorbs at low particle energies almost exclusively through a precursor path; at high beam energies a direct, activated path is used. For the low energy precursor path a dependence on surface temperature is observed. Hydrogen adsorption on the W(110) surface proceeds via a direct activated path. The direct adsorption path for all crystals exhibits a forward directed distribution for the sticking coefficient; in contrast at low particle energies the precursor path shows a minimum of the sticking coefficient in the direction of the surface normal.