Microwave optical double resonance of NO2 with a tunable cw dye laser. II. Excited state microwave transitions

Abstract

Microwave transitions in the 2B2 electronic excited state of NO2 were observed by microwave optical double resonance (MODR) spectroscopy using a tunable, single frequency, continuous wave dye laser as an optical pump. Various spin and hyperfine components of the 909–818 microwave transition in the 2B2 state were identified, and the spin splittings and the hyperfine structure were precisely determined. Interesting pressure dependence of the MODR signal for the 909–818 transition was found and analyzed in terms of a three-level steady state kinetic treatment of microwave optical double resonance. The analysis shows that the 818 level has considerably lower photon yield for photoluminescence than the 909 level. In addition to the 909–818 transitions, three groups of mystery transitions originating from the 909 or 818 level were unexpectedly detected. The final levels of these transitions cannot belong to the same vibronic state as the 909 and 818 states. A reasonable explanation is that the mystery transitions are perturbation induced microwave transitions from levels of the 2B2 state to levels of a longer lived electronic state. Different photon yields of the 909 and 818 rotational levels of the 2B2 state are also understood by perturbations between the 2B2 and the longer lived electronic state.