Infrared spectra of (NO)2- and (NO)2+ isomers trapped in solid neon

Laser-ablation of six different metal targets with concurrent deposition of neon/nitric oxide samples at 4 K produces metal independent absorptions that can be assigned to charged (NO)(2) species. The sharp 1227.3 cm(-1) band and weaker 1225.1 cm(-1) absorption show the different isotopic frequency ratios observed for the argon matrix counterparts at 1221.0 and 1222.7 cm(-1) for trans- (NO)(2)(-) and cis-(NO)(2)(-), respectively. Strong 1619.0 and weaker 1424.1 cm(-1) absorptions, also observed in previous experiments with discharged neon, are enhanced with CCl4 doping while the (NO)(2)(-) bands are diminished, which supports cation identifications. These cation bands reverse absorbance with yellow and near-infrared photolysis. We suggested that the 1619.0 cm(-1) band corresponds to the (NO)(2)(+) isomer made by direct photoionization of cis-(NO)(2). The 1424.1 cm(-1) absorption shares the extreme red photosensitivity found for thermal (NO)(2)(+) ions. Accordingly, the 1424.1 cm(-1) absorption is probably due to the trans isomer, more stable in the gas phase, based on high level calculations, and the 1619.0 cm(-1) band arises from the more stable matrix-isolated cis isomer with a dipole moment, which is produced by the more favorable Franck-Condon photoionization of the cis-(NO)(2) precursor. (C) 1999 American Institute of Physics. [S0021-9606(99)00636-4].