The fluorescence excitation spectrum of rotationally cooled NO2

Abstract

The fluorescence excitation spectrum of NO₂ was measured in the region 5708–6708 Å using a tuneable dye laser as an excitation source. The NO₂ was cooled to a rotational temperature of ∼3 K by expansion with argon as a carrier gas through a supersonic nozzle. This cooling drastically reduced the rotational structure and thereby permitted a clear separation and analysis of 140 vibronic bands found in this 1000 Å region of the spectrum. The results indicate that most of the fluorescence in this region is due to a ²B₂ electronic state, and that this state is so heavily perturbed by high lying levels of the ground electronic state that a substantial fraction of all ground state levels of appropriate vibronic symmetry in this region have appreciable fluorescence intensity.