Infrared spectra of cis and trans-(NO)2- anions in solid argon

Laser-ablation of over 20 different metal targets with concurrent 10 K codeposition of Ar/NO mixtures produces metal independent infrared bands at 1589.3 cm(-1) due to (NO)(2)(+), a new absorption at 1221.0 cm(-1), and a band set at 1300.3, 1222.7, 884.4 cm(-1). The latter bands decrease more on annealing than the 1221.0 cm(-1) band. Isotopic substitution ((NO)-N-14, (NO)-N-15, (NO)-N-15-O-18, and mixtures) shows that these new vibrations involve two equivalent N-O oscillators, which identifies two new (NO)(2) species. The excellent agreement with frequencies, intensities, and isotopic frequency ratios from density functional theory calculations substantiates assignment of the 1221.0 cm(-1) band to trans-(NO)(2)(-) and the three band set to cis-(NO)(2)(-). The observation of a weak combination band at 2492.0 cm(-1) further substantiates assignment of the two N-O stretching modes in cis-(NO)(2)(-). (C) 1998 American Institute of Physics. [S0021-9606(98)02525-2].