By means of a high resolution resonant inelastic x-ray scattering spectroscopy, we have for the first time separated spectral features pertaining to different twoelectron atomic processes in the vicinity of an inner-shell ionization threshold. Contributions of double excitations were extracted from the Ar KM-M2,3M x-ray satellite line intensity measured as a function of photon energy from the 1s3p double core hole threshold to the saturation. The isolated [1s3p]nln'l' excitation spectrum is critically compared to the outcome of the multiconfiguration DiracFock model with relaxation.
COBISS.SI-ID: 22543143
Understanding the role of intermolecular interaction on throughspace charge transfer characteristics in pi-stacked molecular systems is central to the rational design of electronic materials. However, a quantitative study of charge transfer in such systems is often difficult because of poor control over molecular morphology. Here we use the core-hole clock implementation of resonant photoemission spectroscopy to study the femtosecond charge transfer dynamics in cyclophanes, which consist of two precisely stacked pi-systems held together by aliphatic chains. We study two systems, [2,2]paracyclophane (22PCP) and [4,4] paracyclophane (44PCP), with interring separations of 3.0 and 4.0 Å, respectively. We find that charge transfer across the pi-coupled system of 44PCP is 20 times slower than in 22PCP. We attribute this difference to the decreased interring electronic coupling in 44PCP. These measurements illustrate the use of core-hole clock spectroscopy as a general tool for quantifying throughspace coupling in pi-stacked systems.
COBISS.SI-ID: 26125351
We have observed single photon double Kshell photoionization in the C2H2n (n = 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
Experimental evidence for the correlated two electron - one photon transitions 1s^2-)(2s^1)(2p^1), following single-photon K-shell double ionization is reported. The double K-shell vacancy states in solid Mg, Al and Si were produced by means of monochromatized synchrotron radiation, and the TPOE radiative transitions were observed by a wavelength dispersive spectrometer. The TPOE transition energies and branching ratios were determined and compared to predictions of the perturbation theory in the configuration interaction model approach.
COBISS.SI-ID: 24932647
Seeded free electron lasers theoretically have the intensity, tunability, and resolution required for multiphoton spectroscopy of atomic and molecular species. Using the seeded free electron laser FERMI and a novel detection scheme, we have revealed the two-photon excitation spectra of dipole-forbidden doubly excited states in helium. The spectral profiles of the lowest (−1,0)+ 1Se and (0,1)0 1De resonances display energy shifts in the meV range that depend on the pulse intensity. The results are explained by an effective two-level model based on calculated Rabi frequencies and decay rates.
COBISS.SI-ID: 28245799