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Abstract: The absolute photoabsorption cross-section of Ar in the energy region of 50eV through 1100eV has been measured to a high precision using a multi-electrode ion chamber and monochromatized synchrotron radiation. In order to improve the spectral purity of monochromatized synchrotron radiation, an electron storage ring was operated at an electron beam energy that was considerably lower than the normal mode. For most photon energies the obtained photoabsorption cross-sections are in close agreement with data previously reported. However, some discrepancies are noted in the L-shell ionization region. [Copyright &y& Elsevier]

The dissociative multiple photoionization of tetramethylgermane (Ge(CH3)4) in the valence, and in the Ge(3d,3p,3s) and C(1s) inner-shell regions has been studied by using time-of-flight mass spectrometry coupled to synchrotron radiation in the range 49.5–450 eV. Total and individual photoion yields have been recorded as a function of the incident photon energy. Several discrete resonances over a structureless giant resonance are observed below the Ge(3p), Ge(3s) and C(1s) threshold regions. The structureless giant resonance corresponding to the Ge(3d) presumably arises from the continuum enhancement caused by the 3d→∊f transition. Various monocations of H+, H2+, CHn+ (n=0–4), C2Hn+ (n=0–5), GeHn+, GeCHn+, GeC2Hn+, and GeC3Hn+ are detected in the whole energy range. Dissociation processes have also been investigated by photoelectron–photoion and photoion–photoion coincidence methods. The dominant dissociation channel is found to be CHn+–GeCHn+ in the whole energy examined. Specific energy dependence of dissociation processes is observed in the Ge(3p) and Ge(3s) regions. With the help of ab initio HF/6-311++G(2df,p) calculation, we roughly estimated the photoabsorption positions and symmetries for the discrete core hole states. [Copyright &y& Elsevier]

The dissociative multiple photoionization of CBr4 in the valence, and in the Br(3d, 3p, 3s) and C(1s) inner shell regions has been studied by using time-of-flight (TOF) mass spectrometry coupled to synchrotron radiation in the range 50–460 eV. Total and individual photoion yield curves have been recorded as a function of the photon energy. Several discrete resonances are observed below the Br(3d) threshold region. Also a giant shape resonance in the total ion yield curve is observed beyond the Br(3d) region, which can be identified as a shape resonance owing to the diffusion of the outgoing photoelectron by the angular momentum barrier in the 3d9∊f outgoing channel. Various monocations of Br+ and CBrn+ (n=0–3) are detected along with dications of Br2+ and CBr32+ in the whole energy range examined. Dissociation processes of multiply charged CBr4 parent ions have also been investigated by photoelectron–photoion coincidence (PEPICO) and photoion–photoion coincidence (PIPICO) methods. The dominant dissociation pattern is found to involve C+–Br+ and Br+–Br+ in the whole energy range examined. Distinct energy dependence of dissociation processes is observed in the Br(3p) and Br(3s) regions. With the help of ab initio HF/6-311++G(d) calculation, we estimated the photoabsorption positions and symmetries for the discrete core-excited states using the Z+1 equivalent ionic core model. The specific excitation and dissociation of molecules provides information on energy dissipation processes in conjunction with the relevant core hole states. [Copyright &y& Elsevier]

Abstract: A study on Auger-electron spectra of F3SiCH2CH2Si(CH3)3 was performed by using monochromatized synchrotron radiation. The normal Si:L23VV Auger-electron spectrum was measured in the vapor phase and characterized through the ab initio molecular orbital calculation. The cascade Si:L23VV Auger-electron spectra were also obtained by L23-holes creation through Si:KL23L23 Auger transitions after Si:1s photoexcitation in the vapor phase or its photoelectron emission in the condensed phase. Further the C:KVV and F:KVV Auger-electron spectra were measured and discussed in comparison with those of some related molecules. [Copyright &y& Elsevier]

Abstract: Ionic fragmentation caused by Si:1s photoexcitation of 1-trifluorosilyl-2-trimethylsilylethane [F3SiCH2CH2Si(CH3)3] vapor was studied using monochromatized synchrotron radiation and a reflectron-type mass spectrometer. The total ion-yield spectrum in the Si:1s excitation region was found to be very similar to the superposition of the ion-yield spectra of Si(CH3)4 and SiF4, showing that site-specific excitation occurred in this molecule. When the photon energy was scanned from low to high, the 1s→σ* excitation at the Si atom bonded to three CH3 groups suppressed the production of CH3 + and SiCH3 +. The 1s→σ* excitation at the Si atom bonded to three F atoms, on the other hand, enhanced the production of F+ and SiF+ and suppressed the production of SiF3 +. These results suggest that Si:1s site-specific excitation causes site-specific fragmentation. The fragmentation caused by Si:1s→σ* photoexcitation was also found to be more violent than that caused by Si:2p→σ* photoexcitation. [Copyright &y& Elsevier]