Size selective spectroscopy of Se microclusters

The electronic structure and photofragmentation in outer and inner valence regions of Se-n (n <= 8) clusters produced by direct vacuum evaporation have been studied with size-selective photoelectron-photoion coincidence technique by using vacuum-ultraviolet synchrotron radiation. The experimental ionization potentials of these clusters were extracted from the partial ion yield measurements. The calculations for the possible geometrical structures of the Se-n microclusters have been executed. The ionization energies of the clusters have been calculated and compared with the experimental results. In addition, theoretical fragment ion appearance energies were estimated. The dissociation energies of Se-n clusters were derived from the recurrent relation between the gas phase enthalpies of the formation of corresponding cationic clusters and experimental ionization energies. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4737633

Photoelectron recoil in CO in the x-ray region up to 7 keV

Carbon 1s photoelectron spectra of CO molecules in gas phase were recorded in the tender x-ray energy range, from 2.3 to 6.9 keV. The intensity ratios of individual peaks from ν=0 to 3 within the vibrational progression of the C 1s photoelectron spectrum were determined at the various photon energies and are shown to be strongly affected by the photoelectron recoil effect. The experimental vibrational intensity ratios are compared with theoretical predictions at different levels of accuracy. Developments of the recoil model, using generalized Franck-Condon factors, rovibrational coupling, Morse potential energy curves, and accurate angular averaging are presented and applied to the analysis of the experimental results

Coulomb implosion of tetrabromothiophene observed under multiphoton ionization by free-electron-laser soft-x-ray pulses

Soft-x-ray free-electron-laser pulses were used to create highly charged molecular tetrabromothiophene species by sequential multiphoton ionization from bromine 3d orbitals. The experiment was performed at the SACLA facility in Japan and the products of molecular dissociation were analyzed by means of multicoincidence momentum-resolved ion time-of-flight spectroscopy. Total charge states up to +13 atomic units were produced, creating a particular dissociation pattern for the carbon ions, a Coulomb implosion, due to the concerted forces by the surrounding heavy bromine ions. This behavior was explored both experimentally and by numerical molecular-dynamics simulations and the fingerprints of the Coulomb implosion were identified in both. In simulations, Coulomb implosion was predicted to be highly sensitive to the initial (thermal) motion of the atoms and, after including vibrational motion for several temperatures, good general agreement between the experiment and simulations was found. The agreement with the experiment was further improved by adding charge dynamics to the simulation, according to our point-charge dynamics model with empirical rate constants

Photoelectron recoil in CO in the x-ray region up to 7 keV

Carbon 1s photoelectron spectra of CO molecules in gas phase were recorded in the tender x-ray energy range, from 2.3 to 6.9 keV. The intensity ratios of individual peaks from nu = 0 to 3 within the vibrational progression of the C 1s photoelectron spectrum were determined at the various photon energies and are shown to be strongly affected by the photoelectron recoil effect. The experimental vibrational intensity ratios are compared with theoretical predictions at different levels of accuracy. Developments of the recoil model, using generalized Franck-Condon factors, rovibrational coupling, Morse potential energy curves, and accurate angular averaging are presented and applied to the analysis of the experimental results

Effects of molecular potential and geometry on atomic core-level photoemission over an extended energy range: The case study of the CO molecule

We report an experimental and theoretical study of single-molecule inner-shell photoemission measured over an extended range of photon energies. The vibrational intensity ratios I (nu = 1)/I (nu = 0) from the C 1s photoelectron spectra of carbon monoxide, although mostly determined by the bond length change upon ionization, are shown to be affected also by photoelectron recoil and by scattering from the neighboring oxygen atom. Static-exchange density functional theory (DFT) is used to encompass all these effects in a unified theoretical treatment. The ab initio calculations show that the vibrational ratio as a function of the photoelectron momentum is sensitive to both the ground-state internuclear distance and its contraction upon photoionization. We present a proof-of-principle application of DFT calculations as a quantitative structural analysis tool for extracting the dynamic and static molecular geometry parameters simultaneously.Keywords: Diffraction, Photoelectron spectra, Vibrational structure, Photoionizatio