Experimental evidence of a dynamic Jahn-Teller effect in C+60.

Detailed analysis of the highest occupied molecular orbital band shape in the photoelectron spectrum of gaseous C60 reveals a dynamic Jahn-Teller effect in the ground state of C+60. The direct observation of three tunneling states asserts a D3d geometry for the isolated cation, originating from a strong vibronic coupling. These results show that the ionic motion plays an important role in the electron-phonon interaction

Angle-resolved two-dimensional mapping of electron emission from the inner-shell 2p excitations in Cl₂

Angle-resolved Auger and valence photoelectron spectra were measured over a 14-eV photon energy range across the Cl2 2p ionization thresholds. The measurements were carried out using highly efficient time-of-flight spectrometers coupled with photons from the Atomic and Molecular undulator beamline of the Advanced Light Source and an advanced data-acquisition system. Auger-electron spectra of 2→pσ* and 2→pnl resonances were analyzed and the evolution of the resonant Auger to the normal Auger decay distorted by postcollision interaction was examined. We find that valence photoionization channels do not resonate strongly at the photon energies of the core-to-Rydberg excitation, in contrast to the strongly resonating ones observed in the HCl molecule. Auger decay spectra of the 2p−1σ* resonances showed no evidence of atomic transitions in Cl*, also in contrast to HCl. In addition, angular distribution of the photoelectron and Auger-electron lines was derived

Experimental Verification of the Chemical Sensitivity of Two-Site Double Core-Hole States Formed by an X-ray FEL

We have performed X-ray two-photon photoelectron spectroscopy (XTPPS) using the Linac Coherent Light Source (LCLS) X-ray free-electron laser (FEL) in order to study double core-hole (DCH) states of CO2, N2O and N2. The experiment verifies the theory behind the chemical sensitivity of two-site (ts) DCH states by comparing a set of small molecules with respect to the energy shift of the tsDCH state and by extracting the relevant parameters from this shift.Comment: 11 pages, 2 figure

Fragmentation patterns of 4(5)-nitroimidazole and 1-methyl-5-nitroimidazole - The effect of the methylation

We present here the photofragmentation patterns of doubly ionized 4(5)-nitroimidazole and 1-methyl-5-nitroimidazole. The doubly ionized state was created by core ionizing the C 1s orbitals of the samples, rapidly followed by Auger decay. Due to the recent development of nitroimidazole-based radiosensitizing drugs, core ionization was selected as it represents the very same processes taking place under the irradiation with medical X-rays. In addition to the fragmentation patterns of the sample, we study the effects of methylation on the fragmentation patterns of nitroimidazoles. We found that methylation alters the fragmentation significantly, especially the charge distribution between the final fragments. The most characteristic feature of the methylation is that it effectively quenches the production of NO and NO+, widely regarded as key radicals in the chemistry of radiosensitization by the nitroimidazoles

X-ray-initiated photodissociation of the glycine molecule

We investigated the charge distribution and dissociation dynamics of glycine (NH2CH2COOH) molecules irradiated with 310-eV x rays from the Advanced Light Source synchrotron. With simultaneous measurements of the fragment ion yield, dissociation angle, and kinetic energy, we were able to reconstruct a three-dimensional image of the x-ray-initiated molecular dissociation. Using coincidence and correlated analysis and applying a systematic comparison of properties of ion species, we partially disentangled the fragmentation pathways and identified the most probable fragmentation channels that lead to the observed fragment ions. In addition, we showed anisotropic angular distributions of dissociation subsequent to core-level photoionization and Auger decay and found an association between the initial bond-breaking sites and the kinetic energies of the final fragment ions

Spin- and angle-resolved spectroscopy of S2p photoionization in the hydrogen sulfide molecule.

Angle- and spin-resolved photoelectron spectroscopy with circularly and linearly polarized synchrotron radiation were used to study the electronic structure of the hydrogen sulfide molecule. A strong effect of the molecular environment appears in the spin-resolved measurements and, although less clearly, in the angular distribution of the sulfur 2p photoelectrons. The anisotropy and spin parameters of the three main spectral components have been obtained. The validity of simple atomic models in explaining the results is discussed

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