Y Shimizu

Rydberg—valence mixing in the C 1s excited states of CH4 probed by electron spectroscopy

Abstract The C1s → n dt 2 Rydberg series and the ν = 1 vibrational levels of the symmetric mode ( ν 1 ) in the dominant C1s → n pt 2 series are clearly identified in the C 1s high-resolution electron-yield spectrum of CH 4 . In the resonance Auger electron spectra the participant Auger decay rate following the C1s → 3sa 1 , 3pt 2 and 3dt 2 excitations are 5.5%, 2.5%, and 3.7% of the total Auger decays, respectively, indicating that these Rydberg states do not have so strongly mixed valence character. The ordering of the valence contribution as 3sa 1 > 3dt 2 > 3pt 2 is consistent with the theoretical prediction.

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 .

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.

Experimental and theoretical study of the Auger cascade following 3d→5p photoexcitation in Kr

Resonant Auger transitions from the 3d-15p photoexcited states in Kr to the 4s-14p-15p and 4s-25p levels and subsequent Auger decay to the 4p4 and 4s4p5 states of Kr2+ are studied by means of angle-resolved electron spectroscopy. The angular anisotropy parameters β are determined for most of the prominent lines in the spectrum of emitted electrons. It is found that the first-step spectator transitions are strongly anisotropic, while the second-step participator transitions are almost isotropic. Extensive multiconfiguration Dirac-Fock calculations are performed which include correlations in all of the states involved. Noticeable improvements are achieved in comparison with early calculations. The energy position of the main spectral lines and their intensities are described satisfactorily. It turns out that the interference effects due to coherent excitation of resonances influence the anisotropy of the Auger emission significantly. The calculated β parameters agree very well with the experiment.

Auger electron spectra of CF3CN, CF3Cl, CF2Cl2 and CFCl3

Abstract The F KVV and Cl LVV Auger electron spectra of the chlorofluorocarbon molecules CF 3 Cl, CF 2 Cl 2 and CFCl 3 , as well as the F, N and C KVV Auger spectra of the CF 3 CN molecule, have been observed using electron-impact excitation. The spectra have been interpreted with the help of ab initio calculations for the local density of states. The fragmentations specific to the atomic site where the core hole is created, observed for these molecules, are discussed in connection of characters of the Auger final states analyzed in the present study.

A study on multi-charged Xe ions formed through 3d hole states using a coincidence technique

Multiply charged Xe ions produced through photoionization of a 3d electron have been measured using the coincidence technique. The coincidence measurement between the energy-selected Auger electron and ions specifies the individual Auger decay channels for the various multiply charged ions. It has been found that only quadruply charged ions are formed through the Auger decays of M45N45N45 type. The M45N23N45 Auger decays predominantly yield Xe5+. These findings indicate that most Xe ions produced through the initial M45 Auger transitions turn into the highest charge state between energetically accessible states through subsequent successive Auger decays. However, in the M45N1N45 and M45N23N23 decays the intensity ratio of Xe5+ with Xe6+ depends on the energy level of the Auger final states. The highly charged ions, Xe7+ and Xe8+, are produced through the initial Auger shake processes from the 3d hole states. Dedicated to the distinguished contributions to soft x-ray photochemistry research by Professor Inosuke Koyano of the Himeji Institute of Technology on the occasion of his 65th birthday.

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.

Nuclear motion in the O 1s−12πu core-excited states of CO2 probed by sub-natural-width resonant Auger emission spectroscopy

Abstract A promotion of the O 1s electron in the CO2 molecule to the lowest unoccupied molecular orbital 2πu brings about the stretching and bending motions in the core-excited states. These nuclear motions are investigated by use of the sub-natural-width resonant Auger emission spectroscopy.

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.

SYMMETRIES AND DISSOCIATION DYNAMICS OF F 1S CORE EXCITED STATES OF BF3

Using the photoelectron–energy-selected photoion coincidence technique, we find that photoions of BF3 with kinetic energy larger than 4 eV are predominantly F+ in the F 1s ionization region whereas B+ is more intense than F+ at the F 1s→2a2″ excitation. Two partial cross sections σ‖ and σ⊥ for A1′→E′ parallel and A1′→A2″ perpendicular transitions are obtained from the angular distribution measurement of energetic photoions and the symmetries of some F 1s core excited states are confirmed. The dissociation dynamics of the F 1s−12a2″ core excited state are discussed in detail.