First determination of the NO2 Ã 2B2 stretching frequencies by jet cooled intracavity laser absorption spectroscopy around 11 000 cm−1

Abstract

Using intracavity laser absorption spectroscopy combined with a supersonic slit jet, we have observed and analyzed seven vibronic cold bands of NO2 between 10 800 and 11 680 cm−1. The vibronic energies, relative intensities, A, B, and C rotational constants, and the spin-rotation constants have been determined. The rotational constants play a crucial role in the vibronic assignments. The seven observed states are vibronically mixed. However, three of them have a dominant à 2B2 electronic character while the four others have a dominant X̃ 2A1 character. The vibrational assignments and energies of the three à 2B2 levels are: (1, 0, 0) at 10 999.42 cm−1, (0, 2, 0) at 11 210.50 cm−1, and (0, 0, 2) at 11 283.15 cm−1. The frequencies of the symmetric stretch, (ω1≅1265 cm−1), and bending, (ω2≅738 cm−1) modes derived from the (1, 0, 0) and (0, 2, 0) levels are in agreement with ab initio calculations. In contrast, the frequency of the antisymmetric stretch, ω3≅775 cm−1, derived from the observed (0, 0, 2) level, agrees only with the ab initio value obtained by Kaldor while other ab initio values ranging from 390 to 1750 cm−1 were reported. The four levels with a dominant X̃ 2A1 character have been tentatively vibrationally assigned. The present experimental data allows for a first experimental determination of the two à 2B2 stretch vibrational frequencies which are necessary to model the X̃ 2A1–à 2B2 vibronic interactions, i.e., the conical intersection between X̃ 2A1 and à 2B2 potential energy surfaces.