Photoionization of the CO molecule and inner-valence states of CO" between 22 and 45 eV have been studied by means of photoelectron spectroscopy using both synchrotron radiation and He ii radiation. Vibrational structure has been resolved in many bands up to 45 eV. CASSCF (complete active space self-consistent field) and MRCI (multireference configuration interaction) calculations of potential curves in the 22-30 eV range have been perfonned and these have been used to predict vibrational levels and Franck-Condon factors. In this energy range three valence states, D 'IT, 3'E' and 3% have been identified, and spectroscopic constants have been determined for the first two of these. Above 30 eV, all valence slates have been found to be repulsive. In addition to the broad bands expxted for these slates, several progressions of narrow lines are observed most probably reflecting transitions to Rydberg states.P Bultzer et a1 a1 (1994). At higher energies, above approximately 20 eV, the number of states increases quickly due to significant many-electron effects and this leads to a breakdown of the independent-particle molecular orbital approximation. The 3u-' hole state is split into a manifold of ' Z ' stales (Okuda and

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Absolute VUV optical absorption cross sections for ozone have been measured between 325 and 110 nm (3.0 - 11.3 eV) using a synchrotron radiation source. Vibrational fine structure is resolved in Rydberg bands and comparison of this with the limiting bands in the photoelectron spectrum confirms that the order (increasing ionization energy) of the three lowest ionization bands is . Near-threshold electron energy-loss spectra have also been recorded. In these, in addition to the known triplet states between 1 and 2 eV, a low-lying triplet state has been located around 3.4 eV and several others between 6 and 9 eV. Characterization of the valence states (both optically allowed and forbidden) are discussed in relation to the results of early theoretical computations which seem to give a good account of the ozone spectrum.