Single-mode laser fluorescence of NO2 excited at 488 nm

The 488 nm line of the Ar+ laser operated in a single cavity mode excites absorption–fluorescence cycles in which an unusually high proportion exhibit anomalies in the selection rules, including transitions to a1 vibrational levels with values of ΔK = Kinitial – Kfinal of 4,2,0, and −2. Many transitions in the fluorescence, especially the weaker bands, show an intensity distribution different from that expected for type A bands of a 2B2–2A1 transition; this is attributed to interference between the dominant μa moment and a secondary, perpendicular transition moment considered to result from a perturbation of the intermediate state of the cycle by the 2B1 state.Data from about 20 fluorescence bands are used to determine the coefficient of a sextic anharmonic resonance, ν1ν2ν3, ν1, − 3, ν2 + 1, ν3 + 2 in the ground state of NO2.