Adsorption and absorption of hydrogen on a palladium (210) surface: a combined LEED, TDS, Delta Phi and HREELS study

We report on combined LEED, thermal desorption spectroscopy (TDS), work-function ( Delta Phi ), and vibrational loss (HREELS) measurements of the interaction of molecular hydrogen and deuterium with the palladium (210) surface in the temperature range 100-500K. Hydrogen adsorbs spontaneously with a...

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Bibliographic Details
Published in:Surface science 1998-01, Vol.395 (2-3), p.182-204
Main Authors: Christmann, K, Muschiol, U, Schmidt, P K
Format: Article
Language:English
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Summary:We report on combined LEED, thermal desorption spectroscopy (TDS), work-function ( Delta Phi ), and vibrational loss (HREELS) measurements of the interaction of molecular hydrogen and deuterium with the palladium (210) surface in the temperature range 100-500K. Hydrogen adsorbs spontaneously with a very high initial sticking probability as atoms in three binding states denoted as beta sub 3 , beta sub 2 and beta sub 1 , which can be identified with different geometrical adsorption sites. The corresponding activation energies for desorption are around 80, 63 and 45 kJ mol exp -1 , respectively. Exposure at sufficiently low temperatures (120 < =T sub ad < =140K) gives rise to an additional chi TD state at approx150K which cannot be saturated and probably reflects H atoms desorbing from in subsurface and bulk Pd sites, respectively. The most strongly held beta sub 3 state produces a work-function increase of Delta Phi approx =+120 meV. Somewhat less significant Delta Phi contributions of approx+50 meV are caused by the other beta sub 2 and beta sub 1 surface species, while the chi state has absolutely no effect on Delta Phi , which underlines its subsurface character. Likewise, vibrational loss features are only associated with the "surface" hydrogen. The H beta sub 3 -state produces a single broad band at approx56 meV, while both beta sub 2 and beta sub 1 give rise to a second, even broader band at around 88 meV. The chi state is not seen in HREELS. Even at the lowest adsorption temperatures (Tapprox =100K), no H-induced LEED superstructure appears, indicating vanishing long-range order between the adsorbed H atoms and the absence of a H-induced surface reconstruction.
ISSN:0039-6028
DOI:10.1016/S0039-6028(97)00624-9