ASYMMETRY IN THE IONIC FRAGMENTATION OF N2O PHOTOEXCITED AROUND THE N-K AND O-K EDGES

Asymmetry parameters (beta) for the fragment ions of N2O following excitation or ionization of the N and O K shell electrons have been determined from photoelectron-photoion coincidence (PEPICO) and photoion-photoion coincidence (PIPICO) spectra measured using monochromatized synchrotron radiation and a rotatable time-of-flight mass spectrometer. Profiles of the beta parameters from the N+ ions with low kinetic energies (K.E. <4.5 eV) in the PEPICO spectra were found to be very isotropic (close to 0) around both the N and O K edges. 13 parameter profiles for the O+ ions with contributions from N+ ions with K.E. > 4.5 eV and N2+ ions overlapped with NO+ ions show structure with negative values at the pi* resonances below the N K-edges and positive values at the unresolved Rydberg resonances below the terminal N K edge and O K edge and at the shape resonance above the N K edges. beta parameters from the N+-NO+ and N2+-O+ PIPICO signals were found to be considerably more anisotropic than the corresponding values from the PEPICO signals at the pi* resonances below the N K edges and the shape resonance above the ionization edges. Beta parameters from both the PEPICO and PIPICO signals were close to zero at the pi* resonance below the O K edge. The higher degree of anisotropy of ionic fragmentation observed in the PIPICO signals highlights the importance of measuring the fragmentation spectra of polyatomic molecules in coincidence in order to obtain accurate beta parameters.