Infrared Spectrum of the NO₂⁻ Ion Isolated in an Argon Matrix

The molecular ion NO₂⁻ has been stabilized in an argon matrix in sufficient concentration for detection of its antisymmetric stretching fundamental, $ν3$⁠, at 1244 cm⁻¹ by electron bombardment or photoionization of matrix‐isolated NO₂ and by the interaction of an alkali‐metal atomic beam with NO₂ in an argon matrix. In contrast to the position of this fundamental in an inert, nonionic environment, a value of approximately 1275 cm⁻¹ is characteristic of the crystalline material. Isotopic data are consistent with a 115° valence angle for NO₂⁻, independent of environment. Irradiation of the sample with light of wavelength near 3150 Å leads to the destruction of the NO₂⁻ absorption in the studies of the electron bombardment and photoionization of NO₂, but not in the experiments in which the alkali metal atoms provide a reservoir of photoelectrons.