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Université de Fribourg

Absolute angle-differential cross sections for electron-impact excitation of neon within the first 3.5 eV above threshold

Allan, Michael ; Franz, K. ; Hotop, H. ; Zatsarinny, O. ; Bartschat, K.

In: Journal of Physics B: Atomic, Molecular and Optical Physics, 2009, vol. 42, no. 4, p. 044009

Absolute angle-differential cross sections for excitation of neon atoms to the four 2p⁵3s and to selected 2p⁵3p levels have been determined as a function of electron energy up to 3.5 eV above threshold at the scattering angles of 0°, 45°, 90°, 135° and 180°. In addition, the cross sections were recorded as function of scattering angle from 0° to 180° at 18 eV for the 2p⁵3s levels and...

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

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

A dramatic difference between the electron-driven dissociation of alcohols and ethers and its relation to Rydberg states

Ibănescu, Bogdan C. ; Allan, Michael

In: Physical Chemistry Chemical Physics, 2008, vol. 10, p. 5232 - 5237

A difference was observed in the reactivity of alcohols and ethers toward free electrons. Whereas the lowest core-excited state of the negative ion—a ²(n,3s²) Feshbach resonance—of the alcohols readily dissociates by losing a hydrogen atom, ethers show no observable signal from this resonance. This difference in reactivity has a parallel in the anomalous shapes and energies of the...

Université de Fribourg

Absolute cross sections for dissociative electron attachment to acetylene and diacetylene

May, Olivier ; Fedor, Juraj ; Ibănescu, Bogdan C. ; Allan, Michael

In: Physical Review A, 2008, vol. 77, no. 4, p. 040701

Absolute cross sections for the production of the two astronomy-relevant negative ions H−C≡C⁻ and H−C≡C−C≡C⁻ by dissociative electron attachment to acetylene C₂H₂ and diacetylene C₄H₂ were measured (with a ±25% error bar). Acetylene yielded the C₂H⁻ ion at an electron energy of 2.95 eV with a cross section of 3.6±0.9 pm² and also the C₂⁻ ion at 8.1 eV...

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

Absolute angle-differential elastic and vibrational excitation cross sections for electron collisions with tetrahydrofuran

Allan, Michael

In: Journal of Physics B: Atomic, Molecular and Optical Physics, 2007, vol. 40, no. 17, p. 3531

Absolute angle-differential elastic and vibrational excitation cross sections for electron collisions with tetrahydrofuran were measured in the energy range 0.1–20 eV, extending existing measurements to lower energies. The elastic cross sections were measured as a function of scattering angle from 10° to 180° at energies of 2 eV, 6 eV, 10 eV and 20 eV, and as a function of electron energy at...

Université de Fribourg

Electron spectra for associative detachment in low-energy collisions of Cl⁻ and Br⁻ with H and D

Živanov, Svetlana ; Cížek, M. ; Horáček, J. ; Allan, Michael

In: Journal of Physics B: Atomic, Molecular and Optical Physics, 2003, vol. 36, no. 16, p. 3513-3531

Energy spectra of electrons detached in collisions of Cl⁻ and Br⁻ with atomic hydrogen and deuterium have been measured for laboratory frame ion energies between 0.2 and 8.0 eV. Their shapes agree very well with the predictions of nonlocal resonance theory. Both types of structure predicted by the theory are observed. They are the 'v steps', at ro-vibrational thresholds, and the 'S...

Université de Fribourg

Effects of interchannel coupling in associative detachment: electron spectra for H+Cl⁻ and H+Br⁻ collisions

Živanov, Svetlana ; Allan, Michael ; Cížek, M. ; Horáček, J. ; Thiel, F. A. U. ; Hotop, Hartmut

In: Physical Review Letters, 2002, vol. 89, no. 7, p. 073201

We present experimental and theoretical energy spectra of the electrons detached in collisions of slow Cl⁻ and Br⁻ ions with atomic hydrogen. Nonlocal resonance theory predicts two kinds of features in the spectra: steplike structures associated with rovibrational onsets and steep rises associated with interchannel coupling, the latter being absent in a calculation using the simpler...