DESORPTION-KINETICS OF H MO(211)

The desorption kinetics of the H/Mo(211) chemisorption system were stu died by thermal desorption and measurement of adsorption isobars. Anal ysis of the steady-state measurements permits the independent determin ation of the desorption energy (E(d)) and prefactor (nu). These quanti ties are found to depend strongly on coverage, with E(d) varying conti nuously from 145 kJ/mol at low coverage to 65 kJ/mol near saturation. Three regions of hydrogen adsorption are clearly indicated by the isob ars as well as the thermal desorption traces. These regions can be cor related with structural changes observed previously with HREELS and LE ED. The coverage dependence of the kinetic parameters is attributed to hydrogen-induced local distortions of the substrate structure. By rel ating the desorption energy to the isosteric heat the partial molar en tropy is also extracted from the data and indicates localized adsorpti on as well as significant adsorbate-induced changes in the substrate d egrees of freedom.