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About 300 rotational transitions in the 6480 Å region in the visible absorption of NO2 gas have been assigned by laser-excited fluorescence. A majority of the stronger transitions belong to the K = 0 and K = 1 subbands of a vibronic band, T0 = 15 434.9 cm−1, whose upper state is predominantly an a1, vibrational level of the electronic 2B2 basis state. Other groups of relatively weaker lines form (i) a severely-perturbed K = 2 subband attributed to the same series as the K = 0 and 1 subbands; (ii) a well-developed though relatively weak K = 3 subband assigned to a hybrid level of mainly 2A1, character, the transition to this level being induced by vibronic coupling; and (iii) a K = 6 subband assigned to a parent (i.e., 2B2 basis) vibrational level different from that identified at 15 435 cm−1. The spectrum in this region abundantly illustrates the irregularities, 'extra' lines, resonance crossings, and erratic spin splitting now recognized as widespread in the NO2 visible absorption. Rotational constants are not well defined and vary considerably from one subband to another: large pseudo-centrifugal distortion constants are attributed to higher-order effects of the vibronic coupling. Franck–Condon analysis of the intensity distribution in fluorescence leads to a tentative vibrational assignment of 1 60 for the stale at 15 435 cm−1.

The vibrational analysis of the Huggins band system of O3 is reexamined and the electronic transition identified as 1A1 ← 1A1 on the basis that 1–0 and 0–1 transitions in ν3 are widely distributed in the spectrum. Franck–Condon analysis indicates that the 2lA1 state has r = 1.360 Å, θ = 102.4°, corresponding to a longer bond and sharper angle than the ground state structure (r0 = 1.279 Å, θ0 = 116.8°). Estimates of the upper state decay time (2 × 10−13 s) and the f-value of the transition from the ground state (~ 1 × 10−4) are presented. The upper state potential well is considered to result from the avoided crossing of the X1A1(4π) and 21A1(6π) diabatic surfaces.

The intensity of NO2 resonance fluorescence excited at several wavelengths in the range 5930–6480 Å has been measured as a function of final state vibrational quantum numbers. Calculations based on these Franck–Condon profiles establish the relative vibrational assignments of five bands in the [Formula: see text] system. In one case, the similarities between a Ka = 1 and a Ka = 6 profile lead to a value of the à 2B2A rotational constant of ~3.0 cm−1. The influence of Franck–Condon profiles on the radiative lifetime of pure à 2B2 states is investigated.