Photoionisation processes of oxygen and acetylene in the vacuum ultraviolet region

摘要

Photoionisation mass measurements on oxygen and acetylene molecules have been made in the wavelength region from 1100 to 400 A by using synchrotron radiation as a light source. Photoionisation spectra in oxygen are obtained for the molecular ion O2+ and for the fragment ion O+, and in acetylene are obtained for the molecular ion C2H2+ and for fragment ions C2H+, C2+, CH2+ and CH+. To assign the spectral structures of C2H2+, ab initio calculations have been performed for excitation from the second (3δg) and third (2δu) outer molecular orbitals. In the molecular ion spectra of these molecules, several broad structures are observed besides sharp structures due to autoionisation from rydberg states. The broad fetures are discussed in support of theoretical calculations. New Rydberg series (npπu←3δg) converging to the second ionisation threshold were found in the spectra of the molecular ion C2H2+. In the fragment ion spectra, appearance potentials of frabment ions are obtained from onsets of the spectra. Various decay channels after photoionisation are also decided in terms of the onsets.