E Shigemasa

Current status of 10‐m GIM for soft x‐ray undulator at the Photon Factory

The current performance of a 10‐m grazing incidence monochromator (GIM) is described. A resolution of 51, 95, and 220 meV (FWHM) has been achieved at 287, 401, and 867 eV, respectively, inferred from the linewidths for the K‐shell resonances of gaseous CO, N2, and Ne. A photon flux of ≂1012 photons/s is obtainable at the first harmonic of undulator radiation with a 1200‐l /mm grating and 50‐μm slit openings, which correspond to Δλ=0.04 A.

Ionic fragmentation following the 3d core excitation of Sn(CH3)4 by soft X-rays

Abstract Ionic fragmentation following the core-level photoionization of Sn(CH 3 ) 4 has been studied in the photon energy region between 400 and 600 eV by use of monochromatized synchrotron radiation and time-of-flight mass spectrometry. The production of small ionic fragments Sn + , CH m + ( m =0–2), and H + is strongly enhanced by Sn 3d photoionization above 500 eV. Fragmentation processes yielding such small ions are interpreted as decomposition of the multiply charged ion Sn(CH 3 ) 4 q + ( q = 3–5) produced by the vacancy cascade via Auger and/or Coster-Kronig transitions following the Sn 3d photoionization.

Auger-electron—photoion and photoion—photoion coincidence studies on ionic fragmentation of SF6 following the S L-shell excitation

Abstract Auger-electron—photoion coincidence study of SF 6 excited by 196 eV photons shows that the dications having two holes in the outer-valence bands dissociate into various ionic fragments, while those having one hole in the outer-valence and one hole in the inner-valence (F 2s) bands mostly dissociate into atomic ionic fragments F + and S + . Measurement of photoion—photoion coincidence efficiency curves in the S 2p threshold region reveals that not only the S 2p→t 2g and e g excitation above the S 2p threshold but also the S 2p→a 1g excitation below the S 2p threshold enhance the ion-pair formation, suggesting that a considerable part of the resonance-Auger-final states are subject to autoionization.

Threshold behaviour of the multiply-charged photoion yields near the Ar K edge

The authors have measured yield curves of the multiply-charged ions produced by the photoexcitation in the vicinity of the Ar K-shell ionization threshold using monochromatized undulator radiation and a time-of-flight mass spectrometer. The charge distribution of the multiply-charged Ar ions produced by the K-shell excitation suggests that both the electron in the outer shell and the excited Rydberg electron are shaken off with high probability during successive electronic relaxation processes. Post-collision interaction effects are also seen at the photon energies just above the K threshold. The fluorescence yield for the K hole is estimated to be 0.135+or-0.03 from the charge distribution above the K threshold.

Ionic fragmentation of SiH4 following the K-shell excitation

Ionic fragmentation of SiH4 has been studied in the vicinity of the Si: K-edge in the photon energy range 1800-1900eV. Ionic fragments observed at photon energies above the Si: ls → σ* excitation are mostly atomic ions Siq+ (q = 1-3) and H+. Ratios of the abundances for Si+, and Si2+ and Si3+ are roughly 4:4:1, and the abundance of H+ is much higher than the sum of the Si+, Si2+ and Si3+ abundances. The averaged kinetic energy release given to H+ is estimated to be about 12eV. This complete decomposition of SiH4 with the ejection of energetic H+ is interpreted as Coulomb explosion of the multiply-charged (mainly +4 or +5) parent ion produced via the vacancy cascade (successive Auger and/or Coster-Kronig transitions).

Site-specific fragmentation following inner-core level excitation of Pb(CH3)4 in the vapor phase

Abstract Ionic fragmentation following inner-shell (Pb 5p and 4f, C 1 s) excitation of Pb (CH 3 ) 4 has been studied in the vapor phase by use of synchrotron radiation and time-of-flight mass spectrometry. The C 1 s ionization is followed by KVV Auger process, and the fragmentation proceeds by way of the doubly charged parent ion. The Pb 5p or 4f ionization is followed by a cascade of Auger events, and the fragmentation proceeds by way of the triply or higher multiply charged parent ions. The fragmentation pattern changes significantly depending on the site of the core electrons excited (Pb or C).

C 1s and F 1s photoabsorption and subsequent electronic decay of CH4, CH3F, CH2F2, CHF3, and CF4

Abstract High-resolution electron yield spectra of CH4, CH3F, CH2F2, CHF3, and CF4 are observed in the vicinity of C 1s and F 1s thresholds and interpreted with the help of ab initio SCF calculations. Resonance spectator and participant Auger spectra are observed following the C 1s and F 1s excitations of these molecules and discussed in terms of the characters of the orbitals of the electrons involved in the electronic decay. The electronic decay from the fragments is also observed for CH2F2, CHF3, and CF4 at the C 1s → σ ∗ CF antibonding excitation.

Anglar distributions of molecular photofragments emitted following K-shell excitation of N2 and O2

Angle-resolved photoion spectroscopy has been applied to molecular fragments emitted after Auger decay following photoexcitation of the N2 and O2 K-shell in the gas phase. Prominent anisotropic angular-distributions of the fragment ejection, depending strongly on the photon energies, have been observed in the vicinity of the K-shell ionization thresholds.

4d-shell photoionization of Xe, Cs, Ba, Sm, Eu and Yb atoms studied by photoion-yield spectra

A comparative study of multiple photoionization in the 4d ionization region (78-270eV) of M = Xe, Cs, Ba, Sm, Eu and Yb atoms is reported. Partial photion-yield spectra for Mn+ (n = 1-4) ions have been measured by using synchrotron radiation as a light source. Main products in Xe, Cs and Ba are Mn2+ and M3+ ions due to the creation of a 4d vacancy. In Sm and Eu, a large fraction of M+ ions are populated via the 4d-4f resonant excitation and subsequent autoionization to the 4f ionization continuum, which is squeezing the population of multiply-charged ions to about 50%. In Yb, a large amount of M+ ions are also populated, but are due largely to the direct 4f ionization. In all of the atoms studied, an appreciable or considerable amount of M4+ ions are observed, indicating the existence of photoelectron and/or Auger shake-off processes.

Dissociation dynamics of B 1s core-excited BF3 probed by energy-selected electron — energy-selected ion coincidence and angle-resolved ion spectroscopy

A coincidence study between energy-selected electrons and mass- and energy-selected ions shows that dissociation from the spectator-Auger-final states both above and below the double ionization threshold produces energetic B+ whereas dissociation following B 1s ionization produces energetic F+. An angle-resolved photoion study reveals that the B+ is ejected from the spectator-Auger-final states of the deformed C3v pyramidal molecule, after the neutral F ejection but before the free molecular rotations, whereas the B+ ejection following the B 1s ionization is within the D3h plane of the parent molecule.