Photodissociation of NO2 at 157.6 nm

Article abstract of DOI:10.1021/j100293a019

The photodissociation of NO2 has been studied at 157.6 nm, using an F2 laser.The principal products are ground-state NO and O, 4.8 eV of the available energy therefore being disposed of in translational, vibrational, and rotational energy.A total energy balance has not yet been performed, but NO vibrational levels have been detected by laser-induced fluoresence (LIF) in the B²Π-X²Π system in the range ν = 4-21; the thermodynamic limit is ν = 25.Extremely high rotational levels are found in all ground-state vibrational levels.In the most extensively studied level, ν = 5, most of the rotational population is to be found in the N = 50-70 region.Even at the highest vibrational levels, there is little nascent population at the bottom of the rotational manifold.Rotational relaxation of these high levels, where rotational quanta are typically 200 cm^-1, occurs at approximately every collision with helium.NO(B-X) emission, independent of the LIF process, is quite strong and appears to be a consequence of resonances between the F2 laser lines and transitions involving the nascent NO levels produced in the photodissociation.N2(B³Π_g-A³Σ_u⁺) emission is detected, possibly a result of N atom recombination; the most likely source of N atoms is photodissociation and/or photoionization of the excited NO product.Diffuse bands between 770 and 800 nm are also seen, but they have not yet been identified.An attempt was made to determine the selectivity of Λ-doublet production in the NO2 photodissociation process.For unperturbed levels, the splitting seems to be less than our spectral resolution, 0.5 cm^-1, irrespective of rotational level.Much larger effects are expected in transitions to the ν = 1 level of the NO(B) state, which is strongly perturbed by the NO(b⁴Σ^-) state at N = 35-45.Due to spectral contamination by undesired NO(B-X) bands, we have not yet fully resolved the question but are leaning toward the conclusion that both Λ-doublets are produced during photodissociation.