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Université de Fribourg

New light on the Kr⁻(4p⁵5s²) Feshbach resonances: high-resolution electron scattering experiments and B-spline R-matrix calculations

Hoffmann, T. H. ; Ruf, M.-W. ; Hotop, Hartmut ; Zatsarinny, O. ; Bartschat, K. ; Allan, Michael

In: Journal of Physics B: Atomic, Molecular and Optical Physics, 2010, vol. 43, no. 8, p. 085206

In a joint experimental and theoretical effort, we carried out a detailed study of electron scattering from Kr atoms in the energy range of the low-lying Kr⁻($4p^5 5s^2$) Feshbach resonances. Absolute angle-differential cross sections for elastic electron scattering were measured over the energy range 9.3–10.3 eV with an energy width of about 13 meV at scattering angles between 10° and...

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 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...

Université de Fribourg

Isotope effect in dissociative electron attachment to acetylene

May, Olivier ; Fedor, Juraj ; Allan, Michael

In: Physical Review A, 2009, vol. 80, no. 1, p. 012706

Absolute partial cross sections for dissociative electron attachment to H–C≡C–H and D–C≡C–D have been measured using a time-of-flight ion spectrometer combined with a trochoidal electron monochromator. For C₂H₂ the present data are in good agreement with the total cross sections measured previously in our laboratory using the total ion-collection method. The present measurements...

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...