PHOTODISSOCIATION DYNAMICS OF NO-2 AT 248-NM

The dynamics of the photodissociation of NO2 at the excimer wavelength of 248 nm were investigated using a two-laser pump-probe technique. The unrelaxed NO photofragment was probed in vibrational levels 0-9 by (1 + 1) resonantly enhanced multiphoton ionization (REMPI), using the gamma bands of NO in the A2-SIGMA+ <-- X2II transition. From the spectra, the relative populations of the ro-vibrational states of NO were determined. The resulting vibrational distribution was broad and inverted, peaking in upsilon = 5, and also exhibiting a large population in upsilon = 0. The rotational distributions were non-thermal; a clearly bimodal distribution was observed in upsilon = 2. The spin states of NO were equally populated, but a preference was observed for the PI(A') over the PI(A") lambda doublet state. The dynamics of the process, dominated by the deposition of vibrational energy in the NO photofragment, could be qualitatively fitted by a Franck-Condon model, the shape of the vibrational distribution being attributed to the overlap of the vibrational wavefunction of NO in NO2 with that of the NO product.