Inter- and intra-molecular radiationless transitions of NO 2 at around 454.6 nm

Abstract

The continuum emission of NO 2 was investigated on the basis of time-resolved excitation and fluorescence spectra. The analysis of the observed spectra indicated the coexistence of inter- and intra-molecular relaxation processes of NO 2. The continuum emission, the relative intensity of which at longer wavelengths increases more drastically as time goes on after excitation (2–6 μs), was concluded to originate predominantly from molecular collisions in a stepwise deactivation process. A fast component of the continuum emission, with a relative intensity with respect to the discrete band ( I C/ I D) independent of time and of NO 2 pressure, appeared in collision-free conditions (<20 ns, 15 mTorr), and it was concluded to originate from radiationless transitions in isolated molecules.