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Université de Fribourg

Electron-impact vibrational excitation of cyclopropane

Čurík, R. ; Čársky, P. ; Allan, Michael

In: The Journal of Chemical Physics, 2015, vol. 142, no. 14, p. 144312

We report a very detailed test of the ab initio discrete momentum representation (DMR) method of calculating vibrational excitation of polyatomic molecules by electron impact, by comparison of its results with an extensive set of experimental data, covering the entire range of scattering angles from 10∘ to 180∘ and electron energies from 0.4 to 20 eV. The DMR calculations were carried out by...

Université de Fribourg

Vibrational excitation of cyclopropane by electron impact: An experimental test of the discrete-momentum-representation theory with density-functional-theory approximation of polarization and correlation

Čurík, R. ; Čársky, P. ; Allan, Michael

In: Physical Review A - Atomic, Molecular and Optical Physics, 2012, vol. 86, no. 6, p. 062709

The discrete-momentum-representation theory with short-range correlation and polarization approximated by local-density-functional theory has been augmented by connecting the short-range potential to an asymptotic polarization tensor. The capacity of this theory to correctly describe the coupling of a free electron with nuclear motion is tested by a detailed comparison of calculated and measured...

Université de Fribourg

Joint experimental and theoretical study on vibrational excitation cross sections for electron collisions with diacetylene

Čurík, Roman ; Paidarová, Ivana ; Allan, Michael ; Čársky, Petr

In: The Journal of Physical Chemistry A, 2014, vol. 118, no. 41, p. 9734–9744

We have measured and calculated differential and integral cross sections for elastic and vibrationally inelastic electron scattering by diacetylene molecules at electron energies from 0.5 to 20 eV in the whole range of scattering angles from 0 to 180°. The calculations were carried out using the discrete momentum representation method (DMR), which is based on the two-channel Lippmann–Schwinger...

Université de Fribourg

Disentanglement of triplet and singlet states of azobenzene: direct EELS detection and QMC modeling

Dubecký, M. ; Derian, R. ; Horváthová, L. ; Allan, Michael ; Štich, I.

In: Physical Chemistry Chemical Physics, 2011, vol. 13, p. 20939-20945

Singlet and triplet excited states of trans-azobenzene have been measured in the gas phase by electron energy loss spectroscopy (EELS). In order to interpret the strongly overlapping singlet and triplet bands in the spectra a set of large-scale correlated quantum Monte-Carlo (QMC) simulations was performed. The EELS/QMC combination of methods yields an excellent agreement between theory and...

Université de Fribourg

Elastic scattering, vibrational excitation, and attachment in low-energy electron-SF₆ scattering: Experiment and effective range theory

Fabrikant, Ilya I. ; Hotop, Hartmut ; Allan, Michael

In: Physical Review A, 2005, vol. 71, p. 022712-22721

Cross sections at low energies for vibrationally elastic and inelastic scattering, as well as electron attachment to SF₆, have been calculated using a multichannel effective range theory (ERT) with complex boundary conditions. The most active vibrational modes, the totally symmetric mode ν1 and the infrared active mode ν3, have been included in the calculation. The ERT parameters were fitted...

Université de Fribourg

Absolute cross sections for dissociative electron attachment to HCl, HBr, and their deuterated analogs

Fedor, Juraj ; May, Olivier ; Allan, Michael

In: Physical Review A, 2008, vol. 78, p. 032701

We have measured absolute dissociative electron attachment cross sections for HX and DX (X=Cl and Br) using a trochoidal electron spectrometer equipped with a total ion collection collision chamber, operated both in a field-free passive ion collection mode, and an active ion collection mode, with an extracting electric field. Our results for Br⁻ from HBr are in an excellent...

Université de Fribourg

Low-lying resonances in electron-argon scattering: Measurements at 5-meV resolution and comparison with theory

Franz, K. ; Hoffmann, T. H. ; Bömmels, J. ; Gopalan, A. ; Sauter, G. ; Meyer, W. ; Allan, Michael ; Ruf, M.-W. ; Hotop, H.

In: Physical Review A, 2008, vol. 78, no. 1, p. 012712

Combining a laser photoelectron source with a triply differentially pumped supersonic beam target and several electron multipliers for simultaneous detection of electrons elastically scattered into the angles 22.5°, 45°, 90°, 112.5°, and 135° and of metastable atoms due to inelastic scattering, we have carried out an improved study of electron-argon scattering over the energy range...

Université de Fribourg

Low-energy electron attachment to the dichlorodifluoromethane (CCl₂F₂) molecule

Graupner, K. ; Haughey, S. A. ; Field, T. A. ; Mayhew, C. A. ; Hoffmann, T. H. ; May, Olivier ; Fedor, Juraj ; Allan, Michael ; Fabrikant, Ilya I. ; Illenberger, E. ; Braun, M. ; Ruf, M.-W. ; Hotop, Hartmut

In: The Journal of Physical Chemistry A, 2010, vol. 114, no. 3, p. 1474–1484

Results from a joint experimental study of electron attachment to dichlorodifluoromethane (CCl₂F₂) molecules in the gas phase are reported. In a high resolution electron beam experiment involving two versions of the laser photoelectron attachment method, the relative cross section for formation of the dominant anion Cl⁻ was measured over the energy range 0.001−1.8 eV at the gas...

Université de Fribourg

Resonance structure in low-energy electron scattering from OCS

Hoffmann, T. H. ; Hotop, H. ; Allan, Michael

In: Journal of Physics B: Atomic, Molecular and Optical Physics, 2008, vol. 41, no. 9, p. 195202

Energy-dependent absolute angle-differential cross sections (θ = 135°) for elastic and vibrationally inelastic electron scattering from OCS molecules have been investigated at high resolution (13 meV). The elastic cross section, reported over the range E= 0.06–20 eV, exhibits a deep Ramsauer–Townsend minimum near 0.55 eV and the π*(1.2 eV) and σ*(3.8 eV) resonances known from...

Université de Fribourg

Resonance structure in electron–N₂ scattering around 11.5 eV: high-resolution measurements, ab initio calculations and line shape analyses

Hoffmann, T. H. ; Allan, Michael ; Franz, K. ; Ruf, M.-W. ; Hotop, Hartmut ; Sauter, G. ; Meyer, W.

In: Journal of Physics B, 2009, vol. 42, no. 21, p. 215202

Using two different experimental setups with energy widths of about 6 and 13 meV, we obtained significantly improved results for the energy dependence of angle-differential (10°–180°) elastic and vibrationally inelastic cross sections for electron scattering from N₂ molecules in the energy range around the narrow N⁻₂(R²Σ⁺g) resonance. The energy location and the natural...