Affiner les résultats

Type de document

Institution

Collection spécifique

Langue

  • Anglais (59) désactiver le filtre
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

Electron-induced chemistry of alcohols

Ibănescu, Bogdan C. ; May, Olivier ; Monney, Angèle ; Allan, Michael

In: Physical Chemistry Chemical Physics, 2007, vol. 9, p. 3163-3173

We studied dissociative electron attachment to a series of compounds with one or two hydroxyl groups. For the monoalcohols we found, apart from the known fragmentations in the 6–12 eV range proceeding via Feshbach resonances, also new weaker processes at lower energies, around 3 eV. They have a steep onset at the dissociation threshold and show a dramatic D/H isotope effect. We assigned...

Université de Fribourg

Vibrational excitation of hydrogen fluoride by low-energy electrons: theory and experiment

Cízek, M. ; Horáček, J. ; Allan, Michael ; Fabrikant, I. I. ; Domcke, W.

In: Journal of Physics B: Atomic, Molecular And Optical Physics, 2003, vol. 36, no. 13, p. 2837-2849

Vibrational excitation (VE) of HF by low-energy electrons has been investigated experimentally and theoretically. A new nonlocal resonance model has been constructed based on ab initio calculations of the coupling between a discrete state and continuum states. VE and resonant elastic cross sections have been calculated for a set of initial vibrational states of the molecular target. New...

Université de Fribourg

Threshold peaks and structures in elastic and vibrationally inelastic electron impact cross sections for CS₂

Allan, Michael

In: Journal of Physics B: Atomic, Molecular And Optical Physics, 2003, vol. 36, no. 12, p. 2489-2500

Elastic, vibrationally inelastic and superelastic cross sections were measured for electron impact on CS₂ at 135°, with emphasis on the threshold region. The elastic cross section rises dramatically at low energies. The cross sections for the excitation of all three fundamental vibrations (010), (100) and (001) have very strong threshold peaks, more than ten times higher than those observed...

Université de Fribourg

Properties of the π* and σ* states of the chlorobenzene anion determined by electron impact spectroscopy

Skalický, Tomás ; Chollet, Christophe ; Pasquier, Nicolas ; Allan, Michael

In: Physical Chemistry Chemical Physics, 2002, vol. 4, p. 3583 - 3590

The selectivity of vibrational excitation by electron impact has been used to unambiguously assign the negative ion states (resonances) of chlorobenzene and to settle a recent controversy on this subject. The excitation functions of the ring deformation vibrations exhibit bands in the 0.8–1.4 eV range, identifying them as temporary electron captures in the b₁ 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

Decay channels in the dissociative electron attachment to NO

Allan, Michael

In: Journal of Physics B: Atomic, Molecular and Optical Physics, 2004, vol. 37, p. L359-L363

Kinetic energy spectra of O⁻ from dissociative electron attachment (DEA) to NO were measured at 7.6, 8.0, 9.0 and 10.0 eV electron energy using a spectrometer with hemispherical energy selectors for both the incident electrons and the resulting ions. The measurements were performed at 10°, 30°, 90° and 135°. The capacity of the spectrometer to detect both slow and fast ions was verified and...

Université de Fribourg

Electron collisions with NO: Elastic scattering, vibrational excitation, and ²Πi1/2 ⇌ ²Π3/2 transitions

Allan, Michael

In: Journal of Physics B: Atomic, Molecular and Optical Physics, 2005, vol. 38, p. 603

Absolute differential elastic and vibrational excitation cross sections have been measured for NO at 135° with resolution of the ²Π1/2 and ²Π3/2 spin-orbit components of the ground electronic term. The electronic fine structure excitation is dominated by the ³Σ⁻ and the ¹Δ resonances of NO⁻, the nonresonant contribution is very small. The cross section is very large, it has about the...