Nascent NO vibrational distribution from 2485 Å NO2 photodissociation

Abstract

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.