Revisiting NO2 on Ag(1 1 1): a detailed TPD and RAIRS study

The interactions of NO2 with Ag(1 1 1) at various temperatures were investigated by means of temperature programmed desorption and reflection–adsorption infrared spectroscopy and found to be sensitively coverage- and temperature-dependent. During dosing at 508 K, NO2 decomposes into NO(g) and O(a). NO2 decomposes at 215 K also, however, NO and O remain adsorbed. The NO(a) occupy threefold-bridged sites and atop sites in sequence. Orientations of the NO(a) axes are affected by neighboring O(a). A sharp and narrow desorption peak (γ-NO) arises for high NO2 doses. During dosing at 90 K, decomposition occurs initially and is followed sequentially by accumulation of NO2(a), NO3(a), N2O4 monolayer and N2O4 multilayer. NO2(a) chemisorbs to form a Ag(1 1 1) μ-N, O-nitrito surface chelate with Cs symmetry. Upon heating, the N2O4 multilayer and monolayer desorb molecularly while most NO2(a) disproportionates into NO(g) or NO(a) and NO3(a) at 165 K. Surface NO3(a) decomposes below 320 K. All surface species except O(a) desorb below 500 K.