T Hayaishi

Photoionisation mass spectrometric study of acetylene in the VUV region

Photoionisation mass measurements on acetylene have been made between 1100 and 400 AA by using synchrotron radiation as a light source. Photoionisation efficiency curves are obtained for the molecular ion C2H2+ and also for fragment ions C2H+, C2+, CH2+ and CH+. To assign the structures of C2H2+, ab initio calculations have been performed for the excitation from the second (3 sigma g) and third (2 sigma u) occupied molecular orbitals. Two broad maxima at 930 and 810 AA between the first and second ionisation thresholds are assigned to the autoionisation from valence-type excited states. New Rydberg series (np pi u) converging to the second ionisation threshold were found. The appearance potentials of fragment ions by photoexcitation are given and discussed in terms of the heats of formation of molecular ions. For each of C2+ and CH+, two values of the appearance potential are obtained from a double-step structure. The maximum heat of formation of C2+ is estimated from the appearance potential to be 1980 kJ mole-1.

High resolution threshold photoelectron spectroscopy of rare gas dimers

Information on the structure of the ions of neon, argon, krypton and xenon dimers has been obtained using threshold photoelectron spectroscopy and synchrotron radiation under conditions of high resolution. Vibrational structure has been well resolved for the ground state of all these species thus allowing accurate values for the spectroscopic constants to be derived. Structure corresponding to excited states of the dimer ions dissociating to the 2P3/2,1/2 levels of the atomic ion have also been identified and their dissociation energies determined.

Ground and excited states of Xe+2 observed by high resolution threshold photoelectron spectroscopy of Xe2

Threshold photoelectron spectra of the xenon dimer have been observed with a resolution of 2 meV in the wavelength range 920–945 A and 1022–1112 A using the penetrating field technique and synchrotron radiation. Threshold photoelectron bands associated with transitions to the A2 Σ+1/2u, B2 Π3/2g, C2 Π3/2u, C2 Π1/2u, and D2 Σ+1/2g states of Xe+2 have been identified. Vibrational structure associated with the C2 Π1/2u state has been observed for the first time and a new value of the D2 Σ+1/2g state ionization potential is reported.

A high‐flux 3‐M normal incidence monochromator at beamline 20A of the Photon Factory

A high‐flux 3‐m normal incidence monochromator (3‐m NIM) has been installed at beam line 20A of the Photon Factory. The 3‐m NIM can supply a high photon flux in the wavelength region 30–200 nm, primarily because of a large horizontal acceptance angle of 28 mrad for the synchrotron radiation (SR) beam from bending magnet 20. The photon flux of the 3‐m NIM was estimated to be ≊1012 photons/s with Δλ≊0.1 nm at ≊50 nm by measuring the photoemission current from a gold‐coated surface. The resolving power with a 2400 grooves/mm grating was found to be greater than 25 000 at 90 nm from the autoionization profile of the Xe nd’ states converging to Xe+ 2P1/2.

Performance of a varied-space plane-grating monochromator

A new grazing incidence soft x-ray monochromator has been commissioned on the undulator beamline BL-2 of the Photon Factory. The monochromator has been designed to meet the demands for high-resolution soft x-ray spectroscopy. The monochromator has employed a varied space plane grating and a configuration with sagittal focusing and converging beam to satisfy the requirement. According to analytical estimation and ray tracing simulation, the high resolving power beyond 10000 can be obtained over the full energy range from 250 to 1400 eV. Preliminary experiments have been done on three points concerning the resolving power, photon flux, and spot size. The results have showed the typical resolving power from 7500 to 10000, the absolute photon flux ofthe order of lOb photons/s/300mA/O.02%BW, and the spot size ofO.1(V) x 0.9(11) 2FW at the sample position.

Angular correlation between Auger electrons successively emitted from photoexcited resonances in Kr and Xe

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 −1 5/2 5p in Kr and 4d −1 5/2 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.

Vibrational structure of the N+2 ground state observed by threshold photoelectron spectroscopy

The long vibrational progression of the ground state of N+2 was observed in a high resolution threshold photoelectron spectrum obtained using the penetrating field technique and synchrotron radiation. Vibrational states were observed up to v′=67 for the first time and the final vibrational level was deduced to be v′=77 from extrapolation. The complete molecular constants of this state were obtained and the entire potential curve was then drawn.

Vibrational structure of the ground state of Ar2+ by the threshold photoelectron-ion coincidence technique

The coincidence between threshold electrons and ions from Ar2+ was taken to separate the monomer ions and the dimer ions between 790 and 855 AA using synchrotron radiation as a light source. The vibrational structure of the ground state of the Ar2+ ion was clearly observed. The energy of the Ar2+ ionic state is determined to be 116 432+317.2( nu +1/2)-2.5( nu +1/2)2(cm-1) from the zero vibrational state of Ar2.

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.

Decay processes of the C2 2Π1/2u states of Ar2+, Kr2+, and Xe2+

The threshold photoelectron photoion coincidence spectra of the rare gas dimers Ar2, Kr2, and Xe2 have been measured in the photon energy region between the first and second dissociation limits of the dimer ions. It has been found that the C2 2Π1/2u states of Kr2+ and Xe2+ completely dissociate via an optical transition to the repulsive B2 2Π1/2g state, while that of Ar2+ does not dissociate.