The influence of Rydberg states on the photodissociation of nitrous oxide

Abstract

The absolute photoabsorption cross section and the photoionization quantum efficiency of nitrous oxide have been measured from the ionization threshold to 21 eV, using a double ion chamber and monochromated synchrotron radiation, and these have enabled the absolute photodissociation cross section to be deduced. Variations in the photoionization quantum efficiency in the vicinity of a Rydberg state have allowed the competition between predissociation and autoionization in the decay of the super-excited state to be investigated. The photodissociation cross section exhibits prominent structure which correlates with known Rydberg series. Dispersed fluorescence techniques have been employed to identify the electronically excited neutral molecular species (N2 B 3Πg and NO B 2Π) formed through photodissociation of N2O. Fluorescence excitation spectra due to the N2 B 3Πg → A 3Σ+u and the NO B 2Π → X 2Π transitions following excitation of N2O have been recorded and the features in these spectra have been compared with the corresponding structure in the photodissociation spectrum. The N2 B 3Πg fragments are produced directly through photodissociation of the parent molecule. However, at low excitation energies the NO B 2Π fragments are formed only through secondary reactions. The five Rydberg series converging onto the N2O+ C 2Σ+g limit are considered in detail because each series exhibits a specific decay mechanism.