We have observed single photon double K-shell photoionization in the C2H2n (n ¼ 1–3) hydrocarbon sequence and in N2 and CO, using synchrotron radiation and electron coincidence spectroscopy. Our previous observations of the K2 process in these molecules are extended by the observations of a single photon double photoionization with one core hole created at each of the two neighboring atoms in the molecule (K1K1 process). In the C2H2n sequence, the spectroscopy of K1K1 states is much more sensitive to the bond length than conventional electron spectroscopy for chemical analysis spectroscopy based on single K-shell ionization. The cross section variation for single photon K1K1 double core ionization in the C2H2n sequence and in the isoelectronic C2H2, N2 and CO molecules validates a knockout mechanism in which a primary ionized 1s photoelectron ejects another 1s electron of the neighbor atom. The specific Auger decay from such states is clearly observed in the CO case.
COBISS.SI-ID: 27420199
Non-magnetic Pt catalysts, supported on carbon coated magnetic Co nanoparticles, changed catalytic performance in the presence of an external magnetic field. This behavior relates to an electronic change of Pt induced by a localized magnetic field, which modifies the CO adsorption geometry. In situ resonant inelastic X-ray scattering (RIXS) experiments and theory reveal the change of atop CO adsorption geometry on the Pt catalyst to bridged geometry under an external magnetic field. This observation opens the possibility of catalytic control by means of an external magnetic field.
COBISS.SI-ID: 26897191
Two-photon resonant photoionization of helium is investigated both experimentally and theoretically. Ground state helium atoms are excited to the 1s4p, 1s5p and 1s6p 1P states by synchrotron radiation and ionized by a synchronized infrared pulsed picosecond laser. The photoelectron angular distributions of the emitted electrons are measured using a velocity map imaging (VMI) spectrometer. The measured asymmetry parameters of the angular distribution allow the phase differences and the ratios of the dipole matrix elements of the 1ss and 1sd channels to be determined. The experimental results agree with the calculated values obtained in a configuration–interaction calculation with a Coulomb–Sturmian basis set. The effects of the radiative decay of the intermediate state and the static electric field of the VMI spectrometer on the measurements are discussed.
COBISS.SI-ID: 26471975
The dissociation process following the Cl K-shell excitation to σ∗ resonances is studied by high resolution spectroscopy of resonant elastic and inelastic x-ray scattering on CH3Cl, CH2Cl2, CHCl3, and CCl4 molecules. Calculations employing the transition potential and Delta-Kohn-Sham DFT approach are in good agreement with the measured total fluorescence yield and show the presence of a second quasidegenerate group of states with σ∗ character above the lowest σ∗ unoccupied molecular orbital for molecules with more than one Cl atom. A bandwidth narrowing and a nonlinear dispersion behavior is extracted from the Kα spectral maps for both σ∗ resonances. The fitted data indicate that the widths of the Franck-Condon distributions for the first and second σ∗ resonances are comparable for all the molecules under study. In addition, an asymmetric broadening of the emission peaks is observed for resonant elastic x-ray scattering with zero detuning on both σ∗ resonances. This is attributed to the fast dissociation, transferring about 0.15 of the scattering probability into higher vibrational modes.
COBISS.SI-ID: 27146535
Charge transfer through noncovalent interactions is crucial to a variety of chemical phenomena. These interactions are often weak and nonspecific and can coexist, making it difficult to isolate the transfer efficiency of one type of bond versus another. Here, we show how core-hole clock spectroscopy can be used to measure charge transfer through noncovalent interactions. We study the model system 1,4- benzenediamine molecules bound on an Au surface through an Au−N donor−acceptor bond as these are known to provide a pathway for electronic conduction in molecular devices. We study different phases of the molecule/Au system and map charge delocalization times from carbon and nitrogen sites on the molecule. We show that charge delocalization across Au−N donor−acceptor bond occurs in less than 500 as. Furthermore, the Au−N bond also enhances delocalization times from neighboring carbon sites, demonstrating that fast charge transfer across a metal− organic interface does not require a covalently bonded system.
COBISS.SI-ID: 26934567