Université de Fribourg

Coupling of electronic and nuclear motion in a negative ion resonance: Experimental and theoretical study of benzene

Allan, Michael ; Čurík, Roman ; Čársky, Petr

In: The Journal of Chemical Physics, 2019, vol. 151, no. 6, p. 064119

We present calculated and measured elastic and vibrational excitation cross sections in benzene with the objective to assess the reliability of the theoretical method and to shed more light on how the electronic motion of the incoming electron is coupled with the nuclear motion of the vibrations. The calculation employed the discrete momentum representation method which involves solving the...

Université de Fribourg

Dissociative electron attachment and electronic excitation in Fe(CO)5

Allan, Michael ; Lacko, M. ; Papp, P. ; Matejčík, Š. ; Zlatar, Matija ; Fabrikant, Ilya I. ; Kočišek, J. ; Fedor, Juraj

In: Physical Chemistry Chemical Physics, 2018, vol. 20, no. 17, p. 11692–11701

In a combined experimental and theoretical study we characterize dissociative electron attachment (DEA) to, and electronically excited states of, Fe(CO)5. Both are relevant for electron-induced degradation of Fe(CO)5. The strongest DEA channel is cleavage of one metal–ligand bond that leads to production of Fe(CO)4−. High- resolution spectra of Fe(CO)4− reveal fine structures at the...

Université de Fribourg

Recent research directions in Fribourg: nuclear dynamics in resonances revealed by 2-dimensional EEL spectra, electron collisions with ionic liquids and electronic excitation of pyrimidine

Allan, Michael ; Regeta, Khrystyna ; Gorfinkiel, Jimena D. ; Mašín, Zdeněk ; Grimme, Stefan ; Bannwarth, Christoph

In: The European Physical Journal D, 2016, vol. 70, no. 5, p. 1–7

The article briefly reviews three subjects recently investigated in Fribourg: (i) electron collisions with surfaces of ionic liquids, (ii) two-dimensional (2D) electron energy loss spectra and (iii) resonances in absolute cross sections for electronic excitation of unsaturated compounds. Electron energy loss spectra of four ionic liquids revealed a number of excited states, including triplet...

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....

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

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

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...