56 research outputs found
Double photoionization of alkaline earth atoms and photoelectron spectroscopy of reactive intermediates
No full textDouble photoionization (DPI) of the outermost s"2 electrons of Ca and Sr atoms in the vapour phase has been studied by measurements of the angular correlation between the directions of emission of the two electrons. This process has been studied using monochromatic radiation produced by the second generation Daresbury synchrotron radiation source (SRS). The extremely low cross sections of the DPI processes were enhanced by using incident radiation at wavelengths corresponding to autoionizing resonances of the neutral species. Measurements of DPI for Ca atoms have also been collected at a non resonant photon energy using the third generation Elettra SRS in Trieste. Discrepancies between the present experimental results and the limited existing theory are found for the non resonant process. Two-step double photoionization via intermediate excited ionic states has been studied in both Ca and Sr atoms. Measurements of angular distributions and angular correlations between the directions of emission of inner shell photoelectrons and the associated Auger electrons allowed detailed characterizations of the photoionization processes. Valence photoelectron spectroscopy of the short-lived reactive intermediates O_2(a"1#DELTA#_g), OH and OD has been performed using the Daresbury SRS. Autoionizing resonances have been assigned to members of series of Rydberg states converging towards higher ionic limits. Measurements of angular distributions of photoelectrons allowed further insight into the photoionization processes to be obtained. Suggestions are presented for further experimental investigations. (author)SIGLEAvailable from British Library Document Supply Centre-DSC:DXN040244 / BLDSC - British Library Document Supply CentreGBUnited Kingdo
The molecular constants of (CH3I)-C-12 in the ground and nu(6)=1 excited vibrational state
No full textA set of 26 new measurements have been recorded by a Doppler-free double-resonance technique, with a relative accuracy of about 10(-8). These data are combined to previous FTIR measurements to refine the molecular constants of (CH3I)-C-12. All the available literature data have been revisited, a few assignments updated, and some frequencies changed according to new laser standards. A simultaneous fit to all the measurements of infrared, microwave, and radiofrequency transitions produced an improved set of parameters, independent of previously determined constants. (C) 1998 Academic Press
The molecular constants of <sup>12</sup>CH<sub>3</sub>I in the ground and v<sub>6</sub>=1 excited vibrational state
No full textThe beam transport system for the Small Quantum Systems instrument at the European XFEL: optical layout and first commissioning results
No full textThe Small Quantum Systems instrument is one of the six operating instruments of the European XFEL, dedicated to the atomic, molecular and cluster physics communities. The instrument started its user operation at the end of 2018 after a commissioning phase. The design and characterization of the beam transport system are described here. The X-ray optical components of the beamline are detailed, and the beamline performances, transmission and focusing capabilities are reported. It is shown that the X-ray beam can be effectively focused as predicted by ray-tracing simulations. The impact of non-ideal X-ray source conditions on the focusing performances is discussed.Deutsche Forschungsgemeinschaft https://doi.org/10.13039/501100001659Volkswagen Foundation https://doi.org/10.13039/501100001663Horizon 2020 Framework Programme, European Metrology Programme for Innovation and Research https://doi.org/10.13039/100014132Deutsche Forschungsgemeinschaft https://doi.org/10.13039/50110000165
HIGH-RESOLUTION X-RAY STIMULATED RAMAN SPECTROSCOPY USING STOCHASTIC PULSES
No full textX-ray free-electron lasers (XFELs) generate high-intensity x-ray pulses which enable x-ray nonlinear spectro-scopies. The extension of nonlinear spectroscopies to the x-ray domain promises the observation of electronic dynamics on their natural timescales with atomic spatial resolution. Stimulated x-ray Raman spectroscopy is an especially powerful tool, which in a propagation geometry combines large signal enhancement through stimulated emission with ultrahigh energy resolution that overcomes core-hole lifetime broadening. We present high-resolution stimulated Raman spectroscopy realized using stochastic XFEL pulses and correlation techniques. A covariance map between the transmitted SASE pulse and the stimulated Raman scattering produces a high-resolution x-ray Raman spectrum. This promising tool could be applied to study ultrafast electronic and molecular dynamics such as charge transfer in complex systems
Resonant Raman Auger spectroscopy on transient core-excited Ne ions
No full textInternational audienceAbstract Short-lived core-ionized neon atoms were investigated by measuring under resonant Raman conditions the Auger decay following the excitation of a second core electron into a Rydberg state. Making use of intense and narrow bandwidth x-ray free-electron laser pulses, the photoexcitation spectrum of the femtosecond-lived Ne + 1 s 0 2 s 2 2 p 6 n p series was characterized. Energy position and lifetimes of the lower-lying Rydberg states were determined and the final state configurations following the decay of the Ne + 1 s 0 2 s 2 2 p 6 3 p double-core hole resonance were partially resolved
Vibrationally resolved nitrogen K-shell photoelectron spectra of the dinitrogen oxide molecule: Experiment and theory
No full textVibrationally resolved Nc and Nt K-shell photoelectron spectra of the dinitrogen oxide have been studied experimentally and theoretically. Vibrational frequencies for the Nc and Nt 1s ionized states obtained from the 2D potential surfaces computed by the CCSD(T) method within the equivalent core approximation reasonably agree with the experimental values. Experimental relative intensities of the vibrational structure are reasonably reproduced by the multi-channel Schwinger configuration interaction method (MCSCI) with the computed 2D potential surfaces. Improved relaxed geometries of these core–hole states are obtained from fitting the experimental spectra using the MCSCI calculations and regarding the bond lengths as fitting parameters.</p
Core level ionization dynamics in small molecules studied by x-ray-emission threshold-electron coincidence spectroscopy
No full text学術論文 (Article)journal articl
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