Kinetics and Mechanism of NO2 Fluorescence

NO₂ fluorescence experiments with steady or modulated (8 and 20 kHz), monochromatic excitation at 4000–6000 Å and monochromatic observation have shown the process to be interpretable in terms of a single electronically excited state undergoing vibrational relaxation at gas‐kinetic rate and electronic quenching about 100 times more slowly. An apparent radiative lifetime of about 55 μsec was found, independent of excitation frequency, but the possibility of mixing with vibrationally excited ground state makes this an upper limit to the lifetime of the hypothetical unperturbed ${}^2{B}_1$ state. The average amount of vibrational energy transferred per collision was found to be 1000 · 500 cm⁻¹ based on a simplified step‐ladder model for the relaxation.