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

Abstract

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. © 1999 American Institute of Physics.