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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

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

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

Transient anions of cis- and trans-cyclooctene studied by electron-impact spectroscopy

Regeta, Khrystyna ; Nagarka, Amit ; Kilbinger, Andreas F. M. ; Allan, Michael

In: Physical Chemistry Chemical Physics, 2015, vol. 17, no. 6, p. 4696–4700

The effect which deformation of the double bond in trans-cyclooctene (TCO), compared to cis-cyclooctene (CCO), has on its negative ion – and indirectly on the π* virtual orbital – was studied by electron-impact spectroscopy. Differential elastic and vibrational excitation cross sections were measured at a scattering angle of θ = 135°. The vertical attachment energy (VAE) derived from 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

Two-dimensional spectra of electron collisions with acrylonitrile and methacrylonitrile reveal nuclear dynamics

Regeta, Khrystyna ; Allan, Michael

In: The Journal of Chemical Physics, 2015, vol. 142, no. 18, p. 184307

Detailed experimental information on the motion of a nuclear packet on a complex (resonant) anion potential surface is obtained by measuring 2-dimensional (2D) electron energy loss spectra. The cross section is plotted as a function of incident electron energy, which determines which resonant anion state is populated, i.e., along which normal coordinate the wave packet is launched, and of the...

Université de Fribourg

Vibrational excitation of cyclopropane by electron impact: An experimental test of the discrete-momentum-representation theory with density-functional-theory approximation of polarization and correlation

Čurík, R. ; Čársky, P. ; Allan, Michael

In: Physical Review A - Atomic, Molecular and Optical Physics, 2012, vol. 86, no. 6, p. 062709

The discrete-momentum-representation theory with short-range correlation and polarization approximated by local-density-functional theory has been augmented by connecting the short-range potential to an asymptotic polarization tensor. The capacity of this theory to correctly describe the coupling of a free electron with nuclear motion is tested by a detailed comparison of calculated and measured...

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

Vibrational excitation of methane by slow electrons revisited: theoretical and experimental study

Čurík, R ; Čársky, P ; Allan, Michael

In: Journal of Physics B: Atomic, Molecular and Optical Physics, 2008, vol. 41, no. 11, p. 115203

We have calculated and measured differential and integral cross sections for vibrationally inelastic scattering of electrons by methane molecules. The calculations were carried out using the discrete momentum representation (DMR) method. We solved the two-channel Lippmann–Schwinger equation in the momentum space. The interaction between the scattered electron and the target molecule is...

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...