Adsorption or bonding geometries of pure adlayers of several NxOy species, i.e., nitrogen dioxide (NO2), dinitrogen trioxide (N2O3), and dinitrogen tetroxide (N2O4), on Au(111) were determined by utilizing infrared reflection-absorption spectroscopy (IRAS). Dosing NO2 on Au(111) at 85 K produced, in our experiments, mixtures of NO2 and N2O3 (from contaminant NO) at submonolayer coverages and NO2, N2O3, and N2O4 at monolayer coverages. However, a pure adlayer of chemisorbed NO2 could be prepared by forming the monolayer on Au(111) at 85 K and then heating to 185 K or by NO2 exposures on Au(111) at 185 K. Chemisorbed NO2 is bonded to the surface in an O,O′-chelating geometry with C2ν, symmetry. A monolayer of adsorbed N2O3 was produced by exposing the pure, chelating NO2 adlayer to NO(g). The adsorbed complex with N2O3 has Cs symmetry, and we believe that N2O3 is bonded to the surface through one oxygen. Large NO2 exposures can be used to produce crystalline N2O4 multilayers that have a preferential orientation of the N-N bond perpendicular to the Au(111) surface. To probe important aspects of the reactivity of these species with water and to investigate structure-reactivity relationships in this chemistry, we studied the reaction of each of these species with coadsorbed H2O. Upon being heated, reactions proceed via two pathways. One route produces nitrous acid (HONO) and nitric acid (HNO3) and occurs for all of the nitrogen oxide species listed above. These reactions do not depend on the degree of crystallinity of the condensed water clusters. A separate path occurs only for co-condensed amorphous ice clusters and multilayer N2O4 films, as signaled by the formation of oxygen adatoms on the Au(111) surface. These results reveal new information about fundamental interactions of nitrogen oxides and water in condensed phases.
|Original language||English (US)|
|Number of pages||7|
|Journal||Journal of Physical Chemistry A|
|State||Published - Oct 29 1998|
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry