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Université de Fribourg

Recent research directions in Fribourg: nuclear dynamics in resonances revealed by 2-dimensional EEL spectra, electron collisions with ionic liquids and electronic excitation of pyrimidine

Allan, Michael ; Regeta, Khrystyna ; Gorfinkiel, Jimena D. ; Mašín, Zdeněk ; Grimme, Stefan ; Bannwarth, Christoph

In: The European Physical Journal D, 2016, vol. 70, no. 5, p. 1–7

The article briefly reviews three subjects recently investigated in Fribourg: (i) electron collisions with surfaces of ionic liquids, (ii) two-dimensional (2D) electron energy loss spectra and (iii) resonances in absolute cross sections for electronic excitation of unsaturated compounds. Electron energy loss spectra of four ionic liquids revealed a number of excited states, including triplet...

Université de Fribourg

Excited states of Pt(PF₃)₄ andb their role in focused electron beam nanofabrication

Zlatar, Matija ; Allan, Michael ; Fedor, Juraj

In: The Journal of Physical Chemistry C, 2016, vol. 120, no. 19, p. 10667–10674

Electron induced chemistry of metal-containing precursor molecules is central in focused electron beam induced deposition (FEBID). While some elementary processes leading to precursor decomposition were quantitatively characterized, data for neutral dissociation is missing. We provide this data for the model precursor Pt(PF3)4 by using the available cross sections for electronic excitation...

Université de Fribourg

Resonance effects in elastic cross sections for electron scattering on pyrimidine: Experiment and theory

Regeta, Khrystyna ; Allan, Michael ; Winstead, Carl ; McKoy, Vincent ; Mašín, Zdeněk ; Gorfinkiel, Jimena D.

In: The Journal of Chemical Physics, 2016, vol. 144, no. 2, p. 024301

We measured differential cross sections for elastic (rotationally integrated) electron scattering on pyrimidine, both as a function of angle up to 180∘ at electron energies of 1, 5, 10, and 20 eV and as a function of electron energy in the range 0.1–14 eV. The experimental results are compared to the results of the fixed-nuclei Schwinger variational and R-matrix theoretical methods, which...

Université de Fribourg

Absolute cross sections for electronic excitation of pyrimidine by electron impact

Regeta, Khrystyna ; Allan, Michael ; Mašín, Zdeněk ; Gorfinkiel, Jimena D.

In: The Journal of Chemical Physics, 2016, vol. 144, no. 2, p. 024302

We measured differential cross sections for electron-impact electronic excitation of pyrimidine, both as a function of electron energy up to 18 eV, and of scattering angle up to 180°. The emphasis of the present work is on recording detailed excitation functions revealing resonances in the excitation process. The differential cross sections were summed to obtain integral cross sections. These...

Université de Fribourg

Importance of time scale and local environment in electron-driven proton transfer. The anion of acetoacetic acid

Keolopile, Zibo G. ; Gutowski, Maciej ; Buonaugurio, Angela ; Collins, Evan ; Zhang, Xinxing ; Erb, Jeremy ; Lectka, Thomas ; Bowen, Kit H. ; Allan, Michael

In: Journal of the American Chemical Society, 2015, vol. 137, no. 45, p. 14329–14340

Anion photoelectron spectroscopy (PES) and electron energy-loss spectroscopy (EELS) probe different regions of the anionic potential energy surface. These complementary techniques provided information about anionic states of acetoacetic acid (AA). Electronic structure calculations facilitated the identification of the most stable tautomers and conformers for both neutral and anionic AA and...

Université de Fribourg

Two-dimensional spectra of electron collisions with acrylonitrile and methacrylonitrile reveal nuclear dynamics

Regeta, Khrystyna ; Allan, Michael

In: The Journal of Chemical Physics, 2015, vol. 142, no. 18, p. 184307

Detailed experimental information on the motion of a nuclear packet on a complex (resonant) anion potential surface is obtained by measuring 2-dimensional (2D) electron energy loss spectra. The cross section is plotted as a function of incident electron energy, which determines which resonant anion state is populated, i.e., along which normal coordinate the wave packet is launched, and of the...

Université de Fribourg

Excited states at interfaces of a metal-supported ultrathin oxide film

Jaouen, Thomas ; Razzoli, Elia ; Didiot, Clément ; Monney, Gaël ; Hildebrand, Baptiste ; Vanini, Fabiano ; Muntwiler, M. ; Aebi, Philipp

In: Physical Review B, 2015, vol. 91, no. 16, p. 161410

We report layer-resolved measurements of the unoccupied electronic structure of ultrathin MgO films grown on Ag(001). The metal-induced gap states at the metal/oxide interface, the oxide band gap, and a surface core exciton involving an image-potential state of the vacuum are revealed through resonant Auger spectroscopy of the MgKL23L23 Auger transition. Our results demonstrate how to obtain new...