The adsorption of nitric oxide by iron surfaces studied by photoelectron spectroscopy

Abstract

The interaction of nitric oxide at low pressures with iron surfaces in the temperature range 85-290 K has been studied by combined in situ ultraviolet and X-ray induced electron spectroscopy. By monitoring N(1s) and O(1s) binding energies, peak profiles and intensities during nitric oxide interaction regimes of dissociative and molecular adsorption have been recognized. At 85 K adsorption is largely molecular with an N(1s) peak at 400 eV, but some dissociative chemisorption with nitrogen desorption occurs at low coverage indicative of sites of high reactivity and possibly involving intermolecular elimination type reactions. On warming to 290 K further and extensive dissociation occurred, characterized by an N(1s) peak at 397 eV, followed by a small contribution from a pressure dependent weakly adsorbed molecular adsorption of nitric oxide and characterized by an N(1s) value of 401 eV. Information obtained from the O(1s) spectra was in complete accord with that obtained from the N(1s) data. The intensities of the N(1s) and O(1s) spectra enabled estimates to be made of the relative concentrations of nitrogen adatom species under various surface conditions. The interpretation of the molecular processes occurring was strengthened by also comparing peaks in the u. v. induced spectra with those known for NO(g).