INTERACTION OF HYDROGEN WITH RE(10(10)OVER-BAR) - H BINDING STATES AND ORDERED PHASES

LEED, TDS and Delta phi measurements were used to investigate the adso rptive and structural properties of the H-on-rhenium(10 ($) over bar 1 0) system between 120 and 600 K. At all temperatures hydrogen adsorbs dissociatively with high initial sticking probability (s(o) approximat e to 0.7) indicative of a precursor adsorption mechanism. The H satura tion coverage at 120 K reaches 1.63 x 10(19) atoms/m(2); i.e., theta = 2 as referred to Re surface atoms. At saturation, three H binding sta tes appear (alpha, beta(1) and beta(2)) having desorption energies bet ween 60 kJ/mol (alpha) and 125 kJ/mol (beta(2)). These states are inti mately correlated with the H coverage and reflect both the Re-H adsorp tive bond strength and the lateral H-H repulsive interactions. Similar to the Ru(10 ($) over bar 10)/H-system, we observe a c(2x2)-3H phase at theta = 1.5 which slowly transforms to a (1x1)-2H structure as satu ration takes place at theta = 2; however, in contrast to Ru, no other ordered H phases appear for theta < 1.5. Adsorbed H gives rise to an i nitial increase of Delta phi of 370 meV at theta approximate to 0.9, f ollowed by a gentle decrease of approximate to 220 meV, until a stable Delta phi of + 150 meV indicates saturation at theta = 2. Our data ar e discussed and compared with the similar-behaving Ru(10 ($) over bar 10)/H system investigated previously.