The high-resolution He I photoelectron spectrum and the absolute vacuum-ultraviolet (vacuum-UV) absorption cross section (6-25 eV) as well as the ionic fragmentation of chlorine dioxide (OCIO) are reported. The photoelectron spectrum is interpreted in terms of exchange splitting effects of the various singlet and triplet cation states as well as by comparison to chemically related molecules. The vacuum-UV absorption spectrum shows different Rydberg series converging to the cation states. These Rydberg series and their vibrational progressions are assigned by term value arguments, dipole selection rules, and comparison with the photoelectron spectrum. Photoionization mass spectrometry is used for measurements of the ionization and fragmentation threshold of OCIO. The major fragment is C10+ which accurs above 13.4 eV. Thermochemical data such as heats of formation and bond dissociation energies are derived. No evidence for isomerization of OCIO+ is found, as observed for the electronically excited neutral molecule.

Oscillator strengths for the inner-shell excitation (C Is, O Is, Fe 2p, and Fe 3p) of eight gas-phase organoiron complexes Fe(CO)5, Fe2(CO)9, RFe(CO)3 (R = C4He, c-C6H8, c-C8He), and CpFeCpR' (R' = H, C2H3, C4H9) have been derived from electron energy loss spectra recorded under electric dipole scattering conditions. Tentative spectral assignments have been made based upon comparison to the spectra of free ligands and to previous gas-phase studies of related organometallic species. The spectra provide insight into how core excitation spectroscopy reflects the iron-ligand bonding in these complexes. The C Is, 0 Is, and Fe np spectra of related molecules in a series (e.g., carbonyl complexes or ferrocene derivatives) have a similar shape, suggesting similar origins of the spectral features. Small variations through each series have been interpreted in terms of changes in the electronic structure associated with changing substituents. The sensitivity of core spectra to ligand-ligand electronic interaction has been assessed through comparisons to spectral simulations based on the sums of experimental spectra of free ligands and single-ligand complexes. Spectral simulations based on extended Hückel (EHMO) calculations have also been carried out for C Is and Fe 2p excitation in Fe(CO)6 and Fe2(CO)9. The Fe 2p spectra are surprisingly sensitive to the type of ligands present in the complexes.

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Photofragmentation of chlorine dioxide (OC10) and its aggregates is investigated in the UV regime [349-373 nm, A(2A2) -%(2B,) transition]. The products of UV photolysis are subsequently ionized with vacuum UV laser radiation followed by time-of-flight mass analysis. The isolated molecule decays predominantly by formation of vibrationally excited C10 (X(211)) as a result of predissociation. Highly vibrationally excited C10 is formed if even quanta of the asymmetric stretching vibration are excited. The results are discussed in relation to the UV absorption cross section and competitive fragmentation routes, such as formation of molecular oxygen. The UV photolysis of homogeneous chlorine dioxide aggregates [ (OClO),] yields fragments such as excited molecular oxygen, C~ZOS, and C1305. Evidence for evaporation of neutral molecules from excited aggregates is found as well. The results on aggregate photolysis are discussed in relation to experiments on chlorine dioxide in the gas and condensed phase. Ab initio calculations are performed in order to rationalize the experimental results. Properties, such as structures, stabilities, and vibrational frequencies, of different isomers of the OClO dimer and the photolysis product Cl2O3 are derived. Possible implications to stratospheric photochemistry are briefly discussed.

The photostability of C,0D8+ and C10D82+ is investigated between 8 and 35 eV by threshold photoelectron-photoion coincidence (T-PEPICO) measurements using monochromatized synchrotron radiation as excitation source for naphthalene. MNDO calculations were used to interpret photoelectron spectra. The threshold photoelectron spectrum shows evidence of extensive autoionization, considered to be mainly to high vibrational levels of the X2 34Au state of C10D8+. The possibility of a kinetic isotope effect on dissociation is discussed. Fragmentation processes, thresholds, and cutoffs are interpreted. The dissociation rates of the process C10D8+ -* C8D6+ + C2D2 are measured between 16 and 17.7 eV. The results of an RRKM calculation are fitted to the experimental results to give an activation energy of 3.50 eV and activation entropy AS* = -14.1 J/mol-K at 1000 K. A mechanistic model of this dissociation is proposed in terms of two successive C-C bond rupture processes.Appearance potentials determined for the dications C10D82+ (21.5 ± 0.5 eV) and C8D62+ (23.5 ± 0.5 eV) are about 1 eV lower than electron impact values. Application of the results to interstellar polycyclic aromatic hydrocarbons is briefly discussed. Further work with improved mass resolution is proposed. * Experimental work carried out at the LURE Synchrotron radiation facility, Orsay, France.