NO2 jet cooled visible excitation spectrum: Vibronic chaos induced by the X̃ 2A1–Ã 2B2 interaction

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Abstract
Significant improvements have been obtained on measurements of the NO2 jet cooled excitation spectrum in the 16 300–18 502 cm−1 range, previously obtained by Smalley et al. [J. Chem. Phys. 6 3, 4977 (1975)], Persch et al. [Ber. Bunsenges. Phys. Chem. 9 2, 312 (1988)], and Hiraoka et al. [J. Mol. Spectrosc. 1 2 6, 427 (1987)]. The improvements concern first the rotational analysis, owing to a better resolution (150 MHz) and absolute precision (500 MHz), and second the completeness and purity of the resulting vibronic sequence, owing to a better sensitivity. As a result, 159 vibronic energy levels have been observed in the 16 500–18 500 cm−1 energy range, where 210±10 are expected. A detailed comparison with previous results is presented. The statistical analysis of the corresponding energy spacings shows that long range correlations up to 50 mean levels spacings are present, confirming the chaotic behavior of this set of vibronic levels. Furthermore, we analyze the observed rovibronic interactions (or rotational perturbations) that are responsible for the very irregular rotational behavior of the visible absorption spectrum of NO2 at room temperature.