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

Electron energy loss vibrational spectra suggest that hydrogen first adsorbs on Fe(100) in four-fold hollows (β2) and converts to sites of lower ligancy (β1) with increasing coverage. The β1 state desorbs with pseudo first-order kinetics with an activation ener of 14.1 kcal/mol. The β2 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.