The visible excitation spectrum of jet cooled NO2: The chaotic behavior of a set of 2B2 vibronic levels

We have observed a set of 350 2B2 vibronic levels of NO2 in the 16 000–19 360 cm−1 energy range by the laser induced fluorescence (LIF) technique combined with a supersonic jet. This work extends (i.e., a larger energy range) and improves (i.e., a better detection threshold) our previous study [J. Chem. Phys. 95, 5701 (1991)]. 42 new 2B2 vibronic levels have been detected in this range where 159 vibronic levels were previously observed. In the 16 580–19 360 cm−1 energy range we estimate that the 315 observed levels represent 96% of the existing 2B2 levels. The correlation properties of this large and almost complete set of 315 2B2 vibronic levels have been analyzed. We present the next neighbor distribution, the Σ2(L), and Δ3(L) statistics, the Fourier transform (FT) of the stick spectrum with constant intensities (‖FT‖2), and the intensity distribution. The results of these analyses confirm the chaotic behavior of the 2B2 vibronic levels in this energy range: there are strong level repulsion, long range correlations and a Porter–Thomas intensity distribution. The correlation ‘‘hole’’ observed in the ‖FT‖2 of the stick vibronic spectrum is close to the one of the Gaussian orthogonal ensemble (GOE). However we have found a significant deviation from completely chaotic behavior (GOE type). Two peaks in the FT indicate recurrences (periods of 50 and 150 fs) i.e., periodic motions. We conclude that chaos is established within the 2B2 vibronic levels of NO2, after few hundred femtoseconds.