Y. Tamenori

Outline of soft X-ray photochemistry beamline BL27SU of SPring-8

Abstract BL27SU of SPring-8 was constructed for soft X-ray photochemistry. To perform different types of experiments, BL27SU has three branches. In a branch for spectroscopic experiments, a monochromator of very high energy resolving power was required. The other branches were built for experiments in need of high flux rather than energy resolution. In this report the optics and some apparatuses for photochemistry installed in BL27SU are presented.

Symmetry-dependent vibrational excitation in N 1s photoionization of N2 : Experiment and theory

We have measured the vibrational structures of the N 1s photoelectron mainline and satellites of the gaseous N2 molecule with the resolution better than 75 meV. The gerade and ungerade symmetries of the core-ionized (mainline) states are resolved energetically, and symmetry-dependent angular distributions for the satellite emission allow us to resolve the Sigma and Pi symmetries of the shake-up (satellite) states. Symmetry-adapted cluster-expansion configuration-interaction calculations of the potential energy curves for the mainline and satellite states along with a Franck-Condon analysis well reproduce the observed vibrational excitation of the bands, illustrating that the theoretical calculations well predict the symmetry-dependent geometry relaxation effects. The energies of both mainline states and satellite states, as well as the splitting between the mainline gerade and ungerade states, are also well reproduced by the calculation: the splitting between the satellite gerade and ungerade states is calculated to be smaller than the experimental detection limit.

Sub-natural-width angle-resolved resonant Auger electron spectroscopy of atoms and molecules on the high resolution soft X-ray monochromator at SPring-8

Abstract We have installed a high-resolution electron spectroscopy apparatus on the soft X-ray beamline BL27SU at SPring-8 and started the sub-natural-width angle-resolved resonant Auger spectroscopy of atoms and molecules. We demonstrate that the sub-natural-width spectroscopy is a powerful tool both for spectroscopic investigation of the Auger final states and for investigation of the nuclear motion dynamics in the core-excited molecules, presenting some results for the Ne 1s→3p excitation and for the C and O 1s excitations of CO 2 to the lowest unoccupied molecular orbital 2 π u .

Recoil excitation of vibrational structure in the carbon 1s photoelectron spectrum of CF4

The carbon 1s photoelectron spectrum of CF4 measured at photon energies from 330 to 1500 eV shows significant contributions from nonsymmetric vibrational modes. These increase linearly as the photon energy increases. The excitation of these modes, which is not predicted in the usual Franck-Condon point of view, arises from the recoil momentum imparted to the carbon atom in the ionization process. A theory is presented for quantitative prediction of the recoil effect; the predictions of this theory are in agreement to the measurements. The experiments also yield the vibrational frequencies of the symmetric and asymmetric stretching modes in core-ionized CF4, the change in CF bond length upon ionization, -0.61 pm, and the Lorentzian linewidth of the carbon 1s hole, 67 meV.

Hydrogen bonding in methanol clusters probed by inner-shell photoabsorption spectroscopy in the carbon and oxygen K-edge regions

Hydrogen bonding in methanol clusters has been investigated by using inner-shell photoabsorption spectroscopy and density functional theory (DFT) calculations in the carbon and oxygen K-edge regions. The partial-ion-yield (PIY) curves of H(CH(3)OH)(n)(+) were measured as the soft x-ray absorption spectra of methanol clusters. The first resonance peak in the PIY curves, which is assigned to the sigma*(O-H) resonance transition, exhibits a 1.20 eV blueshift relative to the total-ion-yield (TIY) curves of molecular methanol in the oxygen K-edge region, while it exhibits a shift of only 0.25 eV in the carbon K-edge region. Decreased intensities of the transitions to higher Rydberg orbitals were observed in the PIY curves of the clusters. The drastic change in the sigma*(O-H) resonance transition is interpreted by the change in the character of the sigma*(O-H) molecular orbital at the H-donating OH site due to the hydrogen-bonding interaction.

Site-specific fragmentation caused by core-level photoionization in F3SiCH2CH2Si(CH3)3 vapor: Comparison between Si:1s and 2p photoionizations by means of photoelectron-photoion-photoion triple-coincidence spectroscopy

Site-specific fragmentation caused by Si:1s and 2p core-level photoionizations in F(3)SiCH(2)CH(2)Si(CH(3))(3) vapor was studied by energy-selected-photoelectron photoion-photoion triple-coincidence spectroscopy. The difference between the chemical shifts of the two Si sites is larger for the 1s ionization than for the 2p (2s) ionization. The fragmentation caused by the Si:1s ionization is more violent than that caused by the Si:2p ionization. The ions and ion pairs showing high site specificity for the Si:1s ionization belong to small fragments compared to those in the Si:2p ionization. Criteria for high site-specificity in fragmentation are discussed in conjunction with the present results.

Selective detection of tetrahedral units in amorphous GeTe-based phase change alloys using Ge L3-edge x-ray absorption near-edge structure spectroscopy

Using Ge L3-edge x-ray absorption near-edge structure (XANES) studies, we demonstrate a noticeable difference in local structure between amorphous and thermally crystallized GeTe-based phase change alloys. The pronounced change appears as a step-like feature at the absorption edge corresponding to a 2p → 5s (4d) electron transition. Comparison with ab initio XANES simulations suggest that the step-like feature is due to the presence of tetrahedrally coordinated Ge atoms in the as-deposited samples. The obtained results demonstrate that Ge L3-edge XANES can be used as a structural probe for the existence of tetrahedral Ge sites in GeTe-based phase change alloys.

C1s and O1s photoelectron satellite spectra of CO with symmetry-dependent vibrational excitations

The photoelectron shake-up satellite spectra that accompany the C1s and O1s main lines of carbon monoxide have been studied by a combination of high-resolution x-ray photoelectron spectroscopy and accurate ab initio calculations. The symmetry-adapted cluster-expansion configuration-interaction general-R method satisfactorily reproduces the satellite spectra over a wide energy region, and the quantitative assignments are proposed for the 16 and 12 satellite bands for C1s and O1s spectra, respectively. Satellite peaks above the pi(-1)pi(*) transitions are mainly assigned to the Rydberg excitations accompanying the inner-shell ionization. Many shake-up states, which interact strongly with three-electron processes such as pi(-2)pi(*2) and n(-2)pi(*2), are calculated in the low-energy region, while the continuous Rydberg excitations are obtained with small intensities in the higher-energy region. The vibrational structures of low-lying shake-up states have been examined for both C1s and O1s ionizations. The vibrational structures appear in the low-lying C1s satellite states, and the symmetry-dependent angular distributions for the satellite emission have enabled the Sigma and Pi symmetries to be resolved. On the other hand, the potential curves of the low-lying O1s shake-up states are predicted to be weakly bound or repulsive.

Evidence of sequential interatomic decay in argon trimers obtained by electron?triple-ion coincidence spectroscopy

Sequential interatomic decay, where the first step is an Auger decay with interatomic character and the second step is a pure interatomic Coulombic decay (ICD), is identified in Ar trimers Ar3. The 2p hole state in Ar3 decays via the L2,3M1M2,3 Auger to the one-site two-hole states Ar++(3s−13p−1)–Ar–Ar that couples to the two-site satellite states Ar+(3p−2nl)–Ar+(3p−1)–Ar. These states are subject to ICD to the states Ar+(3p−1)–Ar+(3p−1)–Ar+(3p−1), in which the nl electron fills the 3p hole in the same Ar site and one of the 3p electrons in the third Ar site is emitted as a slow ICD electron. This ICD process is identified unambiguously by electron–ion–ion–ion coincidence spectroscopy in which the kinetic energy of the slow ICD electron and the kinetic energy release among the three Ar+ ions are measured in coincidence.

High-resolution angle-resolved ion-yield measurements of H2O and D2O in the region of O 1s to Rydberg transitions

Abstract Angle-resolved energetic-ion yield spectra have been observed in the O 1s excitation region of H2O and D2O with the incident photon-energy resolution better than 14 000 . Vibrational structures appear in most of the Rydberg members and are ascribed to the bending vibrations. The assignments of the electronic states are established on the basis of the angular distribution data for the energetic ions.