Hoshino Masamitsu

We have applied a high-resolution-electron-momentum-resolved-ion coincidence technique to the Auger emission from CF4 following the F 1s→ a(1)(*) excitation and found that the Auger electron emitted from the atomic F fragment during the ultrafast dissociation is backscattered by the residual fragment CF3. We find also that more than half of the excess energy goes into the vibrational excitation of the CF3 fragment.

Ultrafast dissociation of the SF6 molecule following F 1s --> a*(1g) excitation has been studied by the coincident measurement of the kinetic energy of the resonantly emitted electron and the momentum of the fragment ion. The nuclear motion takes place on the same time scale as the Auger decay, leading to atomic-like F (1s)-Auger lines in the electron spectrum. De-tuning from the excitation resonance changes the ratio of the two time scales involved. We measured the shift of the atomic-like Auger line and the changes in the parameters that describe the corresponding ionic fragmentation dynamics as a function of the detuning energy. Our data are consistent with predictions based on electron spectroscopic measurements that resolved the Doppler-splitting of the Auger-line. We found that unlike in diatomic molecules a substantial fraction of the excitation energy remains in the neutral fragment(s).

The lowest-energy satellite bands accompanying the C 1s main line have been investigated, using angle-revolved photoelectron spectroscopy. We find that these satellite bands are resonantly enhanced at the same. photon energy as the shape resonance of the main line. This observation contradicts the predictions based on the shake-up model, and suggests a dominant role of the final state correlations arising from the interaction between a primary photoelectron and a valence electron.

O 1s single-hole ionization cross sections of CO have been measured for v(')=0-2. The O 1s(-1)sigma(*) shape resonance moves up in energy with an increase in v('), opposite to the C 1s(-1)sigma(*) shape resonance observed previously. Theoretical calculations beyond the fixed-nuclei approximation reproduce these experimental results. The relationship between the v(')-dependent characteristic internuclear distance in the residual ion and the shape resonance energy is discussed.

We have studied angular correlations between resonant Auger electrons and successive second-step Auger electrons emitted in a cascade decay after photoexcitation of resonances 3d(5/2)(-1)5p in Kr and 4d(5/2)(-1)6p in Xe. Two spectrometers were used for the angle-resolved detection of the two electrons in coincidence. Angular correlations for several pairs of strong lines have been measured in both atoms. The experimental results are compared with multiconfiguration Dirac-Fock calculations which include electron correlations in the initial, intermediate and final states of the cascade. In general, good agreement between experiment and theory is obtained.

Total cross-sections (TCSs) for electron and positron scattering from C3H4 isomers (allene and propyne) were measured using the linear transmission method in the range of 0.8-600 eV for electrons and 0.7-600 eV for positrons. Elastic cross-sections for electron scattering were also measured by a crossed-beam experiment in the range of 2-100 eV. Sharp resonance-like peaks were observed in the electron TCSs for propyne around 3.6 and 8 eV, and 2.5 and 11 eV for allene. The positron TCSs for these molecules were found to be smaller and much smoother than the electron TCSs. Clear differences in resonance positions and magnitudes between the two isomers can be viewed as an isomer effect. (C) 2002 Elsevier Science B.V. All rights reserved.

Low-energy satellite bands accompanying the C 1s mainline have been investigated both for randomly-oriented and fixed-in-space CO2 molecules. We find that these satellite bands are resonantly enhanced at the same photon energy as the shape resonance of the mainline and more enhanced for the E-symmetry parallel transition than the II-symmetry perpendicular transition. Our observations contradict the predictions based on the shake-up model and agree with predictions given by the photoelectron-impact model which assumes the dominance of final state correlations arising from the interaction between a primary photoelectron and a valence electron.

Absolute differential cross sections (DCSs) for elastic and vibrationally inelastic scattering of electrons from C3H4 isomers (allene and propyne) have been determined by a crossed-beam experiment in the energy range 1.5-100 eV and over the scattering angles between 15degrees-130degrees. The relative flow method was applied to normalize these cross sections, using helium as a standard. Clear evidence of the strong isomer effect has been observed in DCSs for both elastic and vibrational excitation processes, and the isomer effect still conspicuously persists in total elastic cross sections. Two resonance regions where the vibrational cross sections are strongly enhanced are observed in both allene and propyne below a few eV, while both the DCSs become identical at higher energies, hence weakening the isomer effect. More details of the observed mode selectivity are discussed based on the selection rules for vibrational excitation via a shape resonance as well as on an argument based on the angular correlation.

High resolution spectra and angular anisotropy of the resonant Auger electron emission from the 4d(-1)6p photoexcited states in Xe are studied. The low energy part of the spectra which contains transitions to the 5s(1)5p(5)6p and 5s(0)5p(6)6p states of Xe(+) and the subsequent cascade Auger transitions to the 5s(2)5p(4) and 5s5p(5) states of Xe(2+) is investigated in detail. High resolution has enabled us to determine the values of anisotropy parameter beta for many individual resonant Auger transitions and for some second step transitions which had not been measured previously. The results are compared with the theoretical predictions based on the multiconfiguration Dirac-Fock approach.

Absolute differential cross sections (DCSs) for electron impact excitation of electronic states Of CO2 in the 10.8-11.5 eV energy-loss range are reported. These data were obtained at the incident electron energies 20, 30, 60, 100 and 200 eV and over the scattered electron angular range 3.5degrees-90degrees. The accuracy of our experimental methods has been established independently by using several different normalization techniques at both Sophia and Flinders Universities. Generalized oscillator strengths were derived from our measured DCSs and then extrapolated to zero momentum transfer, in order to determine the optical oscillator strengths. These optical oscillator strengths, where possible, are compared with the results from previous measurements and calculations.

The angular distributions of the spin-orbit state resolved S 2p photoelectrons of SF6 have been measured in the vicinity of the shape resonances. Relative partial photoionization cross sections of SF, into the (S 2p(3/2))(-1) and (S 2p(1/2))(-1) states, and the asymmetry parameters of the S 2p(3/2) and S 2p(1/2) photoelectrons are presented. Enhancement of the photoionization cross section into the (S 2p(1/2))(-1) state at the (S 2p(1/2))(-1) 2t(2g) resonance has been observed. The excitation photon energy dependence of the asymmetry parameter shows a broad dip at about the photon energies of the resonances. Continuum multiple-scattering calculation of the asymmetry parameters for the (S 2p(3/2))(-I) and (S 2p(1/2))(-1) states of SF6 reproduces this behavior.

Angular distribution of C2+ ions produced in C4+(1s2) + He → C2+(1s22s2) + He2+ at collision energy of 270 and 470 eV are presented. Measurements have been carried out with an experimental setup for the state selective differential cross section measurements of electron capture processes which utilizes the 14.5 GHz Caprice Electron Cyclotron Resonance (ECR) ion source at RIKEN. It is found that results of calculations based on the potential, which was obtained from the previous experimental results at 1520 eV, do not reproduce the present experimental results at 270 and 470 eV.

Angular distribution of C2+ ions produced in C4+(ls(2)) + He --> C2+(ls(2)2s(2)) + He2+ at collision energy of 270 and 470 eV are presented. Measurements have been carried out with an experimental setup for the state selective differential cross section measurements of electron capture processes which utilizes the 14.5GHz Caprice Electron Cyclotron Resonance (ECR) ion source at RIKEN. It is found that results of calculations based on the potential, which was obtained from the previous experimental results at 1520 eV, do not reproduce the present experimental results at 270 and 470 eV.

We report absolute measurements, using the relative how technique, of low-to-intermediate energy (1.5-100 eV) differential cross sections (DCSs) for elastic electron scattering and vibrational excitation of nitrous oxide. These results, which have been undertaken independently in our two laboratories on different experimental apparatus, are compared in detail with each other and with previous experimental results and theoretical calculations. For elastic scattering the level of agreement between the DCSs from the two laboratories is generally very good. However, the agreement with recent theoretical calculations is rather poor, particularly at energies below 10 eV. For vibrational excitation DCS results have been measured at 2.4 and 8 eV-energies corresponding to the positions of two broad (2)Pi and (2)Sigma shape resonances respectively.