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Université de Fribourg

Absolute angle-differential cross sections for electron-impact excitation of neon atoms from threshold to 19.5 eV

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

In: Journal of Physics B: Atomic, Molecular and Optical Physics, 2006, vol. 39, p. L139-L144

Absolute angle-differential cross sections for electron-impact excitation of neon atoms to the four levels with the (2p⁵3s) configuration have been determined both experimentally and theoretically for incident energies from threshold up to 19.5 eV at scattering angles of 135° and 180°. Excellent agreement between the experimental data and theoretical predictions, obtained by a Breit–Pauli...

Université de Fribourg

Study of resonances in formic acid by means of vibrational excitation by slow electrons

Allan, Michael

In: Journal of Phyics B: Atomic, Molecular and Optical Physics, 2006, vol. 39, no. 14, p. 2939-2947

Absolute differential elastic and vibrational excitation cross sections have been measured for formic acid at 135° from threshold to 5 eV. Most vibrationally inelastic cross sections have a narrow peak at threshold, followed by a broadband with a boomerang structure due to the known π* shape resonance. The cross section for the excitation of the O–H stretch vibration behaves differently, it...

Université de Fribourg

Near-threshold absolute angle-differential cross sections for electron-impact excitation of argon and xenon

Allan, Michael ; Zatsarinny, O. ; Bartschat, K.

In: Physical Review A, 2006, vol. 74, p. 030701

Absolute angle-differential cross sections for electron-impact excitation of argon and xenon atoms to the lowest four np⁵(n+1)s levels, and the 5p⁵5d[7/2]₃ level in xenon, have been measured and calculated as a function of electron energy up to a few eV above threshold at a fixed scattering angle of 135°. For argon, very good agreement is observed...

Université de Fribourg

Electron collisions with formic acid monomer and dimer

Allan, Michael

In: Physical Review Letters, 2007, vol. 98, no. 12, p. 123201

Processes induced by the attachment of slow electrons to formic acid and its hydrogen-bonded dimer were studied. The elastic cross section and the cross section for the excitation of low quanta of discrete vibrations were found to be of a similar magnitude for both targets. A dramatic difference was found in the excitation of a vibrational quasicontinuum in the 1–2 eV range with the ejection of...

Université de Fribourg

Threshold phenomena in electron-molecule scattering

Allan, Michael

In: Physica Scripta, 2004, vol. T110, p. 161-165

Absolute differential cross sections were measured at 135° for the elastic and the vibrationally inelastic electron scattering from threshold to 12 eV, with emphasis on the threshold region. In addition, relative dissociative electron attachment spectra were measured from 0.1 to 3.5 eV. Structures of vibrational origin were observed at energies below 1 eV, well below the ²Π shape resonance, in...

Université de Fribourg

Vibrational structures in electron–CO₂ scattering below the ² Πu shape resonance

Allan, Michael

In: Journal of Physics B: Atomic, Molecular and Optical Physics, 2002, vol. 35, no. 17, p. L387-L395

Structures of vibrational origin were discovered in vibrationally inelastic electron–CO₂ cross sections in the energy range 0.4–0.9 eV, well below the ² Πu shape resonance. They appear in the excitation of higher vibrational levels, in particular the highest members of the Fermi polyads of the type (n, 2m, 0) with n + m = 2–4. The lowest two...

Université de Fribourg

Improved techniques of measuring accurate electron - molecule cross sections near threshold and over a large angular range

Allan, Michael

In: AIP Conference Proceedings, 2007, vol. 901, p. 107-116

Methods to measure absolute differential elastic and vibrational excitation cross sections using an electron spectrometer with a magnetic angle changer are discussed. Emphasized are the need to by-pass drifts and to properly correct for the instrumental response function when angle of detection or electron energy are varied. The results are illustrated with cross sections in nitrogen, methane and...

Université de Fribourg

Electron scattering in ethene: Excitation of the ã³B1u state, elastic scattering, and vibrational excitation

Allan, Michael ; Winstead, C. ; McKoy, V.

In: Physical Review A, 2008, vol. 77, p. 042715

Experimental and calculated absolute differential cross sections for the scattering of low-energy electrons from ethene are presented. Emphasis is on the excitation of the ã³B1u³(π,π*) state, but selected elastic and vibrational excitation cross sections are also given. In contrast to earlier calculations, which were nearly a factor of 2 too large,...

Université de Fribourg

Electron collisions with CO: Elastic and vibrational excitation cross sections

Allan, Michael

In: Physical Review A, 2010, vol. 81, no. 04, p. 042706

Absolute differential elastic and vibrational excitation cross sections up to v=11 were measured for CO in scattering angle ranges extending to 180° at energies between 0.2 and 5 eV (and an elastic measurement at 10 eV). The lowest angles were 0° for inelastic scattering and between 5° and 20° for elastic scattering, depending on energy. Integral cross sections were derived by integrating...

Université de Fribourg

Electron impact excitation of the (4p⁵ 5s) states in krypton: high-resolution electron scattering experiments and B-spline R-matrix calculations

Allan, Michael ; Zatsarinny, O. ; Bartschat, K.

In: Journal of Physics B: Atomic, Molecular and Optical Physics, 2011, vol. 44, no. 6, p. 065201

In a joint experimental and theoretical effort, we carried out a detailed study of electron impact excitation of the 4p⁵ 5s states of Kr. We present angle-differential cross sections over the entire angular range (0°–180°) for a number of energies in the near-threshold region, as well as energy scans for selected angles. The experimental results are in very satisfactory agreement with...