A study has been made of photodissociation processes in O2 which produce autoionizing fragments. Tunable VUV radiation was used to obtain photoelectron spectra. These contain structure due to electron emission from states of atomic oxygen decaying to the ground and first excitated states of the ion. The investigation has concentrated on the region of the thresholds for the production of the atomic autoionization, and spectra have also been recorded up to 60 eV photon energy.

The decay of doubly excited resonances of neutral xenon into all the accessible main line and satellite ionic states has been studied using photoelectron spectroscopy and synchrotron radiation between 20.5 and 26.2 eV. The results show that resonances dominate the satellite cross sections in this region and that they decay selectively into individual J levels of the ion.

Doubly excited neutral states of neon, 2s22p4nln'l', have been investigated using photoelectron spectroscopy with synchrotron radiation. The selective decay of these levels into all the energetically accessible ionic states in the range 50-60 eV has been measured. In addition, decay of Ne+ states, with binding energies above the first double ionisation potential, by autoionisation to the Ne2+(3P) state has been observed.

Autoionising states of atomic oxygen have been observed in the neutral photodissociation of molecular oxygen by synchrotron radiation in the range 19-22 eV. The ejected electrons are measured by high resolution electron spectroscopy and a two-dimensional scanning technique is used to distinguish between atomic electrons produced by autoionisation and photoelectrons produced by exciting vibrational states of the molecule. Autoionising series of atomic oxygen are identified which all decay to the O+ 4S ground state.

Doubly excited neutral states of argon have been investigated by observing their decay into the 3p and 3s main ionisation lines and into the satellite ionic states. These were measured using photoelectron spectroscopy and monochromatic synchrotron radiation in the range 31.0 to 42.3 eV. The 3p and 3s main line constant ionic state spectra show structure due to the decay of doubly excited states but in general these are much less prominent than in the spectra for the satellites which are dominated by resonances, particularly close to threshold. There is also a strong selectivity with marked differences in the resonance structure observed in the decay to different satellite states. Four Rydberg progressions have been observed each of which is split into two series.

A photoelectron spectrometer which incorporates a position-sensitive detector and differential pumping has been used to investigated the X2Πg state of the molecular chlorine ion. Photon energies were chosen such that ionisation occurred via intermediate autoionising states. This significantly altered the vibrational distribution of the final ionic state enabling accurate determination of the vibrational constants (ωe = 79.6 meV, ωeχe = 0.37 meV) and the spin-orbit splitting (86.3 meV) for the X2Πg state. The autoionising states between 13.6–14.15 eV have also been studied and new vibrational progressions identified.

Vibrationally resolved photoelectron spectra of hydrogen chloride have been measured as a function of photon energy from 13.25 to 16.65 eV using monochromatic synchrotron radiation and a spectrometer incorporating a position-sensitive detector. Excitation functions for the first 12 vibrational states of the X 2 Pi ionic state are obtained and from these functions three Rydberg progressions converging to the A 2 Sigma + excited state are identified. A comparison is made between the experimental branching ratios of the X 2 Pi ionic state vibrational levels and the results of a model calculation of Terwilliger and Smith (1975).