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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

Isotope effect in dissociative electron attachment to acetylene

May, Olivier ; Fedor, Juraj ; Allan, Michael

In: Physical Review A, 2009, vol. 80, no. 1, p. 012706

Absolute partial cross sections for dissociative electron attachment to H–C≡C–H and D–C≡C–D have been measured using a time-of-flight ion spectrometer combined with a trochoidal electron monochromator. For C₂H₂ the present data are in good agreement with the total cross sections measured previously in our laboratory using the total ion-collection method. The present measurements...

Université de Fribourg

Absolute dissociative electron attachment cross sections in acetylene and its deuterated analogue

May, Olivier ; Fedor, Juraj ; Allan, Michael

In: Chimia, 2010, vol. 64, no. 3, p. 173-176

An instrument for the measurement of absolute dissociative electron attachment cross sections was constructed and applied to two prototype molecules, acetylene (C₂H₂) and deuterated acetylene (C₂D₂). The isotope effect at the first dissociative electron attachment band at 3 eV was determined-the cross section for C₂D⁻/C₂D₂ is 14.4 times smaller than that for C₂H⁻/C₂H₂. The...

Université de Fribourg

Absolute cross sections for dissociative electron attachment to HCN and DCN

May, Olivier ; Kubala, D. ; Allan, Michael

In: Physical Review A, 2010, vol. 82, p. 010701

Absolute partial cross sections for the formation of CN⁻ in dissociative electron attachment to HCN and DCN have been measured using a time-of-flight ion spectrometer combined with a trochoidal electron monochromator to be 940pm² for CN⁻/HCN and 340pm² for CN⁻/DCN at peaks of the bands due to the ²Π-shape resonance. The dissociative electron attachment bands were then recorded under...

Université de Fribourg

Dissociative electron attachment to Pt(PF₃)₄—a precursor for Focused Electron Beam Induced Processing (FEBIP)

May, Olivier ; Kubala, Dušan ; Allan, Michael

In: Physical Chemistry Chemical Physics, 2012, no. 9, p. 2979-2982

Experimental absolute cross sections for dissociative electron attachment (DEA) to Pt(PF₃)₄ are presented. Fragment anions resulting from the loss of one, two, three and four PF₃ ligands as well as the Pt(PF₃)F⁻ and the F⁻ ions were observed. The parent anion Pt(PF₃)⁻₄ is too short-lived to be detected. The dominant process is loss of one ligand, with a very large cross section...

Université de Fribourg

Absolute cross sections for electronic excitation of furan by electron impact

Regeta, Khrystyna ; Allan, Michael

In: Physical Review A, 2015, vol. 91, no. 1, p. 012707

We measured differential cross sections for exciting the three lowest electronically excited states in furan, as functions both of electron energy and of scattering angle. Emphasis of the present work is on recording detailed excitation functions, revealing resonances in the excitation process. The cross section for the first triplet state has a shoulder in the first 2 eV above threshold,...

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

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

Free electrons and ionic liquids: study of excited states by means of electron-energy loss spectroscopy and the density functional theory multireference configuration interaction method

Regeta, Khrystyna ; Bannwarth, Christoph ; Grimme, Stefan ; Allan, Michael

In: Physical Chemistry Chemical Physics, 2015, p. -

The technique of low energy (0–30 eV) electron impact spectroscopy, originally developed for gas phase molecules, is applied to room temperature ionic liquids (IL). Electron energy loss (EEL) spectra recorded near threshold, by collecting 0–2 eV electrons, are largely continuous, assigned to excitation of a quasi-continuum of high overtones and combination vibrations of low-frequency modes....