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Université de Fribourg

Absolute angle-differential vibrational excitation cross sections for electron collisions with diacetylene

Allan, Michael ; May, Olivier ; Fedor, Juraj ; Ibănescu, Bogdan C. ; Andric, L.

In: Physical Review A, 2011, vol. 83, p. 052701

Absolute vibrational excitation cross sections were measured for diacetylene (1,3-butadiyne). The selectivity of vibrational excitation reveals detailed information about the shape resonances. Excitation of the C≡C stretch and of double quanta of the C-H bend vibrations reveals a ²Πu resonance at 1 eV (autodetachment width ~30 meV) and a ²Πg resonance at 6.2 eV...

Université de Fribourg

Absolute cross sections for electron collisions with diacetylene: elastic scattering, vibrational excitation and dissociative attachment

Allan, Michael ; May, Olivier ; Fedor, Juraj ; Ibǎnescu, Bogdan C ; Andrić, Lidija ; Winstead, Carl ; McKoy, Vincent

In: Journal of Physics: Conference Series, 2012, vol. 388, no. 5, p. 052082

We present absolute experimental cross sections for elastic scattering, vibrational excitation by electron impact and for dissociative electron attachment to 1,3-butadiyne, as well as calculations of the elastic cross sections.

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

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

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

Cleavage of the ether bond by electron impact: differences between linear ethers and tetrahydrofuran

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

In: Physical Chemistry Chemical Physics, 2008, vol. 10, p. 1507-1511

Dissociative electron attachment (DEA) to diethyl ether yielded primarily the C₂H₅O⁻ ion, with a strong Feshbach resonance band at 9.1 eV and a weaker shape resonance band at 3.89 eV. Very similar spectra were obtained for dibutyl ether, with C₄H₉O⁻ bands at 8.0 and 3.6 eV. Some of these primary ions subsequently lost H₂ and yielded weaker signals of the C₂H₃O⁻ and...

Université de Fribourg

Experimental evidence on the mechanism of dissociative electron attachment to formic acid

Janečková, Radmila ; Kubala, Dušan ; May, Olivier ; Fedor, Juraj ; Allan, Michael

In: Physical Review Letters, 2013, vol. 111, no. 21, p. 213201

Two mechanisms for dissociative electron attachment in HCOOH, the formation of HCOO−+H, were proposed in the literature: (i) via a direct electron attachment into a σ∗ resonance, augmented by dipole binding of the incident electron [G. A. Gallup et al., Phys. Rev. A 79, 042701 (2009)], and (ii) with the 1.8 eV π∗ resonance as a doorway state, linked to the products by...

Université de Fribourg

Partial cross sections for dissociative electron attachment to tetrahydrofuran reveal a dynamics-driven rich fragmentation pattern

Janečková, Radmila ; May, Olivier ; Milosavljević, A.R. ; Fedor, Juraj

In: International Journal of Mass Spectrometry, 2014, vol. 365–366, p. 163–168

We report partial absolute cross sections for dissociative electron attachment (DEA) to tetrahydrofuran C₄H₈O. The high sensitivity of the present setup, quantitative DEA spectrometer with time-of-flight analyzer, led to identification of a number of previously unreported fragments (CH₂⁻, OH⁻, CHO⁻, C₄H₅O⁻, C₃H₃⁻) thus revealing complex dissociation dynamics of the...

Université de Fribourg

Dissociative electron attachment to methylacetylene and dimethylacetylene: Symmetry versus proximity

Janečková, Radmila ; May, Olivier ; Fedor, Juraj

In: Physical Review A - Atomic, Molecular, and Optical Physics, 2012, vol. 86, no. 05, p. 052702

We have measured absolute dissociative electron attachment (DEA) cross sections in methylacetylene (propyne, C₃H₄) and dimethylacetylene (but-2-yne, C₄H₆). The main feature in the low-energy DEA spectrum is a π* shape resonance giving rise to fragments at 3.4 eV in C₃H₄ and 4.0 eV in C₄H₆. The process C₃H₄+e→ C₃H₃ −+H proceeds via abstraction...