A STUDY OF THE ABSOLUTE PHOTOABSORPTION CROSS-SECTION AND THE PHOTOIONIZATION QUANTUM EFFICIENCY OF NITROUS-OXIDE FROM THE IONIZATION THRESHOLD TO 480-ANGSTROM

The absolute photoabsorption cross section and the photoionization quantum efficiency of nitrous oxide have been measured using a double ion chamber and monochromated synchrotron radiation. In the wavelength range encompassed by the present study the cross section is dominated by intense structure associated with Rydberg series converging onto either the A 2-SIGMA+ or the C2-SIGMA+ ionization thresholds. Neutral predissociation from these excited molecular states causes significant variations to be observed in the photoionization quantum efficiency. The results indicate that decay from a particular Rydberg member tends to produce an effect on the photoionization quantum efficiency that is characteristic of the series to which that member belongs. The data are discussed in relation to recent theoretical work studying the competition between neutral predissociation and autoionization.