Nascent NO vibrational distribution from 2485 Å NO2 photodissociation

The initial NO vibrational level distribution has been determined for NO2 photodissociation at 2485 Å. Excitation spectra of the NO vibrational levels were measured by using both the NO A 2Σ+←X 2Π and B 2Π←X 2Π transitions, the latter being somewhat stronger due to saturation effects. It was determined that the NO population was strongly inverted, with most of the nascent NO being in v=6–8; the thermodynamic limit is v=8. Injection locking of the KrF laser output permitted study of the 2491 Å NO2 band, and it was evident that the increased absorption in this region gave greatly enhanced signal levels in the excitation spectra, at those wavelengths where NO2 and NO absorption lines coincide. It was demonstrated that in the 2640–2850 Å wavelength region, NO2 can be detected by use of a single dye laser, simultaneously dissociating NO2 and electronically exciting the resultant vibrationally hot NO. Deactivation of NO(v=8) by NO2 was found to proceed with a rate coefficient of 1.1×10−11 cm3 molecule−1 s−1, whereas the coefficient for quenching by N2 and He was ≤2×10−15 cm3 molecule−1 s−1. The peculiar NO rotational distributions noted by Zacharias et al. in their study of NO2 dissociation at 3371 Å were also observed in the present work.