Hydrogen bonding on iron: Correlation of adsorption and desorption states on Fe(100) and perturbation of the Fe-H bond with coadsorbed CO

Electron energy loss vibrational spectra suggest that hydrogen first adsorbs on Fe(100) in four-fold hollows (beta(2)) and converts to sites of lower ligancy (beta(1)) with increasing coverage. The beta(1) state desorbs with pseudo first-order kinetics with an activation energy of 14.1 kcal/mol. The beta(2) state exhibits a vibrational frequency of 700 cm(-1), indicative of adsorption in four-fold hollows. With increasing coverage this mode is replaced by a vibration at 1000 cm(-1), indicative of conversion of adsorbed H to an asymmetric position within the four-fold hollow. Adsorption of CO onto the H-covered surface causes an increase in the frequency of the mode near 1000 cm(-1) associated with movement to a position of lower ligancy within the four-fold hollow.