Characterization of Single and Pairwise NO2 Adsorption on the (Mgo)9 and (Cao)9 Clusters

摘要

Vibrational spectra have been computed by means of the B3LYP hybrid density functional in order to interpret the experiments [J. Phys. Chem. B 2002, 106, 6358], particularly regarding a transient 1225 cm~(-1) absorption during accumulation of NO2 in MgO supported BaO. The degree of generality of results is tested by comparing (NO2)_x(MO)9 for x=l, 2 and M=Mg, Ca. Finger prints are produced for the single bidentate M~(2+)-[ONO]~--M~(2+) surface nitrite ion, a novel single monodentate [O_(clus)-NO2]~(2-) ion, and the chemisorbed nitriteitrate ion pair, i.e., M~(2+) -[ONO]~--M~(2+)+ [O_(clus)-NO2]~-. The results suggest the novel monodentate [O_(clus)- NO2]~(2-) to be responsible for the experimentally observed 1225 cm~(-1) absorption, being a transient towards surface nitrate rather than nitrite formation. This result is consistent with a mechanistic periodic DFT study concerning the initial loading of NO2 in BaO.