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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

The assignment of dissociative electron attachment bands in compounds containing hydroxyl and amino groups

Skalický, Tomás ; Allan, Michael

In: Journal of Physics B: Atomic, Molecular and Optical Physics, 2004, vol. 37, p. 4849-4859

Dissociative electron attachment (DEA) spectra were recorded for methanol, phenol, diethylamine, tetramethylhydrazine, piperazine, pyrrole and N,N-dimethylaniline. Comparison with He I photoelectron spectra permitted the assignment of virtually all DEA bands in the saturated compounds to core excited Feshbach resonances with double occupation of Rydberg-like orbitals and various Koopmans' states...

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...

Université de Fribourg

Transitions between the ²Π₁͵₂ and ²Π₁͵₃ spin-orbit components of NO induced by impact of slow electrons

Allan, Michael

In: Physical Review Letters, 2004, vol. 93, p. 063201-63204

The electron impact cross section for the transition between the ²Π₁͵₂ and ²Π₁͵₃ spin-orbit components of the ground electronic term of nitric oxide, separated by 15 meV, has been measured as a function of electron energy at a scattering angle of Θ= 135°. It is dominated by the ³Σ⁻ and the ¹Δ resonances. Its magnitude is very large, at peak about equal to that of the elastic...

Université de Fribourg

Excitation of the four fundamental vibrations of CH₄ by electron impact near threshold

Allan, Michael

In: Journal of Physics B: Atomic, Molecular and Optical Physics, 2005, vol. 38, p. 1679

Absolute differential elastic and vibrational excitation cross sections have been measured for CH₄ at 90° and from 0.1 to 1.5 eV, with the resolution of all four vibrational modes. Threshold peaks were observed in the excitation of the ν1, ν3 and ν4 modes, but not in the ν2 mode. These results are in good agreement with the recent calculation of Nishimura and Gianturco (2002 J. Phys. B:...