Molecular predissociation of nitrogen dioxide studied by fluorescence excitation spectroscopy

Abstract

In a steady-state experiment, fluorescence efficiency of the electronically excited nitrogen dioxide has been measured in the pressure range of 1–1000 mTorr and in the exciting wavelength range of 3800–5200 Å using 0.1–1.0 Å resolution. It was found to be independent of the exciting wavelength in the 4150–5200 Å range, but began to decline sharply below 4150 Å. Since the dissociation limit of the ground state NO₂ giving the ground states of NO and O corresponds to 3979 Å, this early onset of “predissociation” is attributed to the utilization of the rotational energy in overcoming the dissociation threshold. Probable radiationless transitions involving the excited NO₂ molecules are discussed in light of the higher resolution data on the fluorescence excitation efficiencies.