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Université de Fribourg

Excited states of Pt(PF₃)₄ andb their role in focused electron beam nanofabrication

Zlatar, Matija ; Allan, Michael ; Fedor, Juraj

In: The Journal of Physical Chemistry C, 2016, vol. 120, no. 19, p. 10667–10674

Electron induced chemistry of metal-containing precursor molecules is central in focused electron beam induced deposition (FEBID). While some elementary processes leading to precursor decomposition were quantitatively characterized, data for neutral dissociation is missing. We provide this data for the model precursor Pt(PF3)4 by using the available cross sections for electronic excitation...

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

Growth of ice nanoparticles via uptake of individual molecules: pickup cross sections

Fedor, Juraj ; Lengyel, Jozef ; Kočišek, J. ; Poterya, V. ; Pysanenko, A. ; Svrčková, P. ; Fárník, M.

In: Journal of Physics: Conference Series, 2014, vol. 488, no. 10, p. 102016

We present cross sections for pickup of several atmospherically relevant molecules on ice nanoparticles with the 0.5-3 nm diameter range. The experimental values are supported by molecular dynamics simulations and analytical calculations based on long-range cluster-molecule potentials. The cross sections are all considerably larger than the geometrical cross section of nanoparticle and vary...

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

Electron impact excitation of methane: determination of appearance energies for dissociation products

Danko, M. ; Orszagh, J. ; Ďurian, M. ; Kočišek, J. ; Daxner, M. ; Zöttl, S. ; Maljković, J. B. ; Fedor, Juraj ; Scheier, P. ; Denifl, S. ; Matejčík, Š.

In: Journal of Physics B: Atomic, Molecular and Optical Physics, 2013, vol. 46, no. 4, p. 045203

In this work, we present an experimental study of dissociative excitation of CH₄ utilizing a crossed electron molecular beam experiment. Methane was excited by nearly monochromatic electrons generated by a trochoidal electron monochromator. The dissociative products were identified on the basis of the emission spectra in the ultraviolet–visible (UV/VIS) spectral range. The excitation...

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...

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

Uptake of atmospheric molecules by ice nanoparticles: Pickup cross sections

Lengyel, J. ; Kočišek, J. ; Poterya, V. ; Pysanenko, A. ; Svrčková, P. ; Fárník, M. ; Zaouris, D. K. ; Fedor, Juraj

In: Journal of Chemical Physics, 2012, vol. 137, p. 034304

Uptake of several atmospheric molecules on free ice nanoparticles was investigated. Typical examples were chosen: water, methane, NOx species (NO, NO₂), hydrogen halides (HCl, HBr), and volatile organic compounds (CH₃OH, CH₃CH₂OH). The cross sections for pickup of these molecules on ice nanoparticles (H₂O)N with the mean size of ***Missing image...

Université de Fribourg

Oxidation of sterols: energetics of C–H and O–H bond cleavage

Lengyel, Jozef ; Rimarčík, Ján ; Vagánek, Adam ; Fedor, Juraj ; Lukeš, Vladimír ; Klein, Erik

In: Food Chemistry, 2012, vol. 133, no. 4, p. 1435–1440

Phytosterols, as components of human diet, received much attention because of their cholesterol-lowering and antioxidant properties. We have theoretically studied sterols oxidation in terms of O–H and C–H bond dissociation enthalpies (BDE). In 17 Δ⁵- and Δ⁷-sterols, BDEs were obtained for reported sites of oxidation attack. Obtained results indicate that Δ⁷-sterols are more...