## Publications

Export 69 results:
Sort by: Author Title Type [ Year ]
2016
Neustetter, Michael, Filipe Ferreira da Silva, and Stephan Denifl. "{Electron interactions with the focused electron beam induced processing (FEBID) precursor tungsten hexachloride}." RAPID COMMUNICATIONS IN MASS SPECTROMETRY. 30 (2016): 1139-1144. Abstract

RationaleSecondary electrons with an energy distribution below 100 eV are formed when high-energy particles interact with matter. In the focused electron beam induced deposition, high-energy beams are used to decompose organometallic compounds on surfaces. We investigated the electron ionisation of WCl6 and dissociative electron attachment to WCl6 in the gas phase in order to better understand the decomposition mechanism driven by secondary electrons. MethodsA double-focusing mass spectrometer coupled with a Nier-type ion source was used to perform the present studies. The electron ionisation studies were performed with an electron energy of 70 eV and dissociative electron attachment studies in the energy range of similar to 0-14 eV. ResultsTungsten hexachloride rapidly oxidises, leading to the formation of a mixture of pure WCl6 and WCl4O together with WCl2O2 species. The fragmentation of the three chlorinated compounds is effective, although electron ionisation to WCl6 leads to W+ in contrast with WCl2O2 and WCl4O leading to WO2+ and WO+, respectively, as lighter fragments. With regard to electron attachment, decomposition of the precursor molecules is observed; however, W- was not detected within the detection limit of the instrument. ConclusionsElectron ionisation and dissociative electron attachment (DEA) to WCl6, WCl4O and WCl2O2 lead to strong fragmentation. In electron ionisation, the fragmentation by loss of chlorine atoms was observed for both WCl6 and the oxidised species. Additionally, the loss of all chlorine ligands is observable for WCl6 as well as the oxidised species. The DEA results have shown dissociation by the scission of chlorine atoms as well as by the scission of an oxygen atom. The formation of chlorine and oxygen anions was observed, indicating the formation of a neutral counterpart containing the metal atom, free to be attacked by the next electron. Copyright (c) 2016 John Wiley {&} Sons, Ltd.

Rebelo, Andre, Tiago Cunha, Monica Mendes, Filipe Ferreira da Silva, Gustavo Garcia, and Paulo Limao-Vieira. "{Kinetic-energy release distributions of fragment anions from collisions of potassium atoms with D-Ribose and tetrahydrofuran}." EUROPEAN PHYSICAL JOURNAL D. 70 (2016). Abstract

Kinetic-energy release distributions have been obtained from the width and shapes of the time-of-flight (TOF) negative ion mass peaks formed in collisions of fast potassium atoms with D-Ribose (DR) and tetrahydrofuran (THF) molecules. Recent dissociative ion-pair formation experiments yielding anion formation have shown that the dominant fragment from D-Ribose is OH {\{}[{\}}D. Almeida, F. Ferreira da Silva, G. Garcia, P. Limao-Vieira, J. Chem. Phys. 139, 114304 (2013)] whereas in the case of THF is O{\{}[{\}} D. Almeida, F. Ferreira da Silva, S. Eden, G. Garcia, P. Limao-Vieira, J. Phys. Chem. A 118, 690 (2014)]. The results for DR and THF show an energy distribution profile reminiscent of statistical degradation via vibrational excitation and partly due to direct transformation of the excess energy in translational energy.

Limao-Vieira, P., D. Duflot, F. da Silva, E. Lange, N. C. Jones, S. V. Hoffmann, M. A. Smialek, D. B. Jones, and M. J. Brunger. "{Valence and lowest Rydberg electronic states of phenol investigated by synchrotron radiation and theoretical methods}." JOURNAL OF CHEMICAL PHYSICS. 145 (2016). Abstract

We present the experimental high-resolution vacuum ultraviolet (VUV) photoabsorption spectra of phenol covering for the first time the full 4.3-10.8 eV energy-range, with absolute cross sections determined. Theoretical calculations on the vertical excitation energies and oscillator strengths were performed using time-dependent density functional theory and the equation-of-motion coupled cluster method restricted to single and double excitations level. These have been used in the assignment of valence and Rydberg transitions of the phenol molecule. The VUV spectrum reveals several new features not previously reported in the literature, with particular reference to the 6.401 eV transition, which is here assigned to the 3s sigma/sigma{\{}*{\}}(OH) {\textless}- 3 pi(3a `') transition. The measured absolute photoabsorption cross sections have been used to calculate the photolysis lifetime of phenol in the earth's atmosphere (0-50 km). Published by AIP Publishing.

Matsui, Midori, Masamitsu Hoshino, Hidetoshi Kato, Fillipe Ferreira da Silva, Paulo Limao-Vieira, and Hiroshi Tanaka. "{Measuring electron-impact cross sections of water: elastic scattering and electronic excitation of the (a)over-tilde(3)B(1) and (A)over-tilde(1)B(1) states}." EUROPEAN PHYSICAL JOURNAL D. 70 (2016). Abstract

Here, we report elastic differential cross sections (DCSs) for electron scattering from water in the incident energy range of 2-100 eV. Furthermore, we present a complete study on the electronic excitation of the (a) over tilde B-3(1) and (A) over tilde B-1(1) states at electron impact energies of 15, 20, and 30 eV and in the scattering angle range of 10. -130.. Integral cross sections (ICSs) are determined from the DCSs. Measuring elastic DCSs in various experimental conditions confirmed the reproducibility of the data. The present results agree with the data previously obtained from a conventional collimating tube gas source. Ambiguities associated with the unfolding procedure of the electron energy loss (EEL) spectra for the electronic excitations have been reduced by comparison against the EEL spectrum at high electron impact energy and for small scattering angle. The reliability of the extracted DCSs is improved significantly for optically forbidden contributions from the overlap of the (a) over tilde B-3(1) and (A) over tilde B-1(1) electronic states. The BEf-scaling model is also confirmed to produce the integral cross section for the optical allowed transition of the (A) over tilde B-1(1) state in the intermediate electron energy region above 15 eV.

Pastega, D. F., E. Lange, J. Ameixa, A. S. Barbosa, F. Blanco, G. García, M. H. F. Bettega, P. Limão-Vieira, and F. {Ferreira Da Silva}. "{Combined experimental and theoretical study on the differential elastic scattering cross sections for acetone by electron impact energy of 7.0-50 eV}." Physical Review A - Atomic, Molecular, and Optical Physics. 93 (2016). Abstract

© 2016 American Physical Society.We report elastic differential cross sections (DCSs) for electron interactions with acetone, C3H6O. The incident electron energy range was 7.0-50 eV, and the scattered electron angular range for the differential measurements varied from 10° to 120°. The calculated cross sections were obtained with two different methodologies, the Schwinger multichannel method with pseudopotentials (SMCPP), and the independent-atom method with screening-corrected additivity rule (IAM-SCAR). The present elastic DCSs have been found to agree well with the results of IAM-SCAR calculations above 20 eV, and also with the SMC calculations below 30 eV. Although some discrepancies were found for lower energies, the agreement between the SMCPP data and the DCSs obtained with the IAM-SCAR method improves, as expected, as the impact energy increases. Comparison with previous DCSs shows good agreement albeit the present data is extended down to lower electron impact energies. We find a low-lying $π$∗ shape resonance located at 2.6 eV, in agreement with recent results on electron collisions with acetone [M. G. P. Homem et al., Phys. Rev. A 92, 032711 (2015)10.1103/PhysRevA.92.032711]. The presence of a $\sigma$∗ resonance is also discussed.

{Ferreira Da Silva}, F., G. Meneses, O. Ingólfsson, and P. Limão-Vieira. "{Side chain effects in reactions of the potassium-tyrosine charge transfer complex}." Chemical Physics Letters. 662 (2016): 19-24. AbstractWebsite
n/a
2015
da Silva, Ferreira F., E. Lange, P. Limao-Vieira, N. C. Jones, S. V. Hoffmann, M. - J. Hubin-Franskin, J. Delwiche, M. J. Brunger, R. F. C. Neves, M. C. A. Lopes, E. M. de Oliveira, R. F. da Costa, M. T. N. do Varella, M. H. F. Bettega, F. Blanco, G. Garcia, M. A. P. Lima, and D. B. Jones. "{Electronic excitation of furfural as probed by high-resolution vacuum ultraviolet spectroscopy, electron energy loss spectroscopy, and ab initio calculations}." JOURNAL OF CHEMICAL PHYSICS. 143 (2015). Abstract

The electronic spectroscopy of isolated furfural (2-furaldehyde) in the gas phase has been investigated using high-resolution photoabsorption spectroscopy in the 3.5-10.8 eV energy-range, with absolute cross section measurements derived. Electron energy loss spectra are also measured over a range of kinematical conditions. Those energy loss spectra are used to derive differential cross sections and in turn generalised oscillator strengths. These experiments are supported by ab initio calculations in order to assign the excited states of the neutral molecule. The good agreement between the theoretical results and the measurements allows us to provide the first quantitative assignment of the electronic state spectroscopy of furfural over an extended energy range. (C) 2015 AIP Publishing LLC.

Ribar, Anita, Marian Danko, Juraj Orszagh, Filipe Ferreira da Silva, Ivo Utke, and Stefan Matejcik. "{Dissociative excitation study of iron pentacarbonyl molecule (vol 69, 117, 2015)}." EUROPEAN PHYSICAL JOURNAL D. 69 (2015). Abstract
n/a
Limao-Vieira, P., F. da Silva, D. Almeida, M. Hoshino, H. Tanaka, D. Mogi, T. Tanioka, N. J. Mason, S. V. Hoffmann, M. - J. Hubin-Franskin, and J. Delwiche. "{Electronic excitation of carbonyl sulphide (COS) by high-resolution vacuum ultraviolet photoabsorption and electron-impact spectroscopy in the energy region from 4 to 11 eV}." JOURNAL OF CHEMICAL PHYSICS. 142 (2015). Abstract

The electronic state spectroscopy of carbonyl sulphide, COS, has been investigated using high resolution vacuum ultraviolet photoabsorption spectroscopy and electron energy loss spectroscopy in the energy range of 4.0-10.8 eV. The spectrum reveals several new features not previously reported in the literature. Vibronic structure has been observed, notably in the low energy absorption dipole forbidden band assigned to the (4 pi {\textless}- 3 pi) ((1)Delta {\textless}- (1)Sigma(+)) transition, with a new weak transition assigned to ((1)Sigma(-) {\textless}- (1)Sigma(+)) reported here for the first time. The absolute optical oscillator strengths are determined for ground state to (1)Sigma(+) and (1)Pi. transitions. Based on our recent measurements of differential cross sections for the optically allowed (spectroscopy and (1)Pi) transitions of COS by electron impact, the optical oscillator strength f(0) value and integral cross sections (ICSs) are derived by applying a generalized oscillator strength analysis. Subsequently, ICSs predicted by the scaling are confirmed down to 60 eV in the intermediate energy region. The measured absolute photoabsorption cross sections have been used to calculate the photolysis lifetime of carbonyl sulphide in the upper stratosphere (20-50 km). (C) 2015 AIP Publishing LLC.

da Silva, F., D. Duflot, S. V. Hoffmann, N. C. Jones, F. N. Rodrigues, A. M. Ferreira-Rodrigues, G. G. B. de Souza, N. J. Mason, S. Eden, and P. Limao-Vieira. "{Electronic State Spectroscopy of Halothane As Studied by ab Initio Calculations, Vacuum Ultraviolet Synchrotron Radiation, and Electron Scattering Methods}." JOURNAL OF PHYSICAL CHEMISTRY A. 119 (2015): 8503-8511. Abstract

We present the first set of ab initio calculations (vertical energies and oscillator strengths) of the valence and Rydberg transitions of the anaesthetic compound halothane (CF3CHBrCl). These results are complemented by high-resolution vacuum ultraviolet photoabsorption measurements over the wavelength range 115-310 nm (10.8-4.0 eV). The spectrum reveals several new features that were not previously reported in the literature. Spinorbit effects have been considered in the calculations for the lowest-lying states, allowing us to explain the broad nature of the 6.1 and 7.5 eV absorption bands assigned to sigma{\{}*{\}}(C-Br) {\textless}- nBr and sigma{\{}*{\}}(C-Cl) {\textless}- n(Cl) transitions. Novel absolute photoabsorption cross sections from electron scattering data were derived in the 4.0-40.0 eV range. The measured absolute photoabsorption cross sections have been used to calculate the photolysis lifetime of halothane in the upper stratosphere (20-50 km).

Oller, J. C., L. Ellis-Gibbings, F. da Silva, P. Limao-Vieira, and G. Garcia. "{Novel experimental setup for time-of-flight mass spectrometry ion detection in collisions of anionic species with neutral gas-phase molecular targets}." EPJ TECHNIQUES AND INSTRUMENTATION. 2 (2015). Abstract

We report a novel experimental setup for studying collision induced products resulting from the interaction of anionic beams with a neutral gas-phase molecular target. The precursor projectile was admitted into vacuum through a commercial pulsed valve, with the anionic beam produced in a hollow cathode discharge-induced plasma, and guided to the interaction region by a set of deflecting plates where it was made to interact with the target beam. Depending on the collision energy regime, negative and positive species can be formed in the collision region and ions were time-of-flight (TOF) mass-analysed. Here, we present data on O-2 precursor projectile, where we show clear evidence of O- and O-2(-) formation from the hollow cathode source as well as preliminary results on the interaction of these anions with nitromethane, CH3NO2. The negative ions formed in such collisions were analysed using time-of-flight mass spectrometry. The five most dominant product anions were assigned to H-, O-, NO-, CNO- and CH3NO2- .

Serralheiro, C., D. Duflot, Ferreira F. da Silva, S. V. Hoffmann, N. C. Jones, N. J. Mason, B. Mendes, and P. Limao-Vieira. "{Toluene Valence and Rydberg Excitations as Studied by ab initio Calculations and Vacuum Ultraviolet (VUV) Synchrotron Radiation}." JOURNAL OF PHYSICAL CHEMISTRY A. 119 (2015): 9059-9069. Abstract

The electronic spectroscopy of isolated toluene in the gas phase has been investigated using high-resolution photoabsorption spectroscopy in the 4.0-10.8 eV energy range, with absolute cross-section measurements derived. We present the first set of ab initio calculations (vertical energies and oscillator strengths), which we use in the assignment of valence and Rydberg transitions of the toluene molecule. The spectrum reveals several new features not previously reported in the literature, with particular relevance to 7.989 and 8.958 eV, which are here tentatively assigned to the pi{\{}*{\}}(17a' {\textless}- sigma(15a') and 1 pi{\{}*{\}}(10a{\{}''{\}}) {\textless}- 1 pi(14a') transitions, respectively. The measured absolute photoabsorption cross sections have been used to calculate the photolysis lifetime of toluene in the upper stratosphere (20-50 km).

Limao-Vieira, P., G. Meneses, T. Cunha, A. Gil, M. J. Calhorda, G. Garcia, and Ferreira F. da Silva. "{Complex internal rearrangement processes triggered by electron transfer to acetic acid}." XXIX INTERNATIONAL CONFERENCE ON PHOTONIC, ELECTRONIC, AND ATOMIC COLLISIONS (ICPEAC2015), PTS 1-12. Eds. C. {Diaz, I. Rabadan, G. Garcia, L. Mendez, and F. } Martin. Vol. 635. Journal of Physics Conference Series, 635. Univ Autonoma Madrid; Consejo Super Investigaciones Cient, 2015. Abstract

We present negative ion formation from collisions of 100 eV neutral potassium atoms with acetic acid (CH3COOH) and its deuterated analogue molecules (CH3COOD, CD3COOH). From the negative ion time-of-flight (TOF) mass spectra, OH-is the main fragment detected accounting on average for more than 25{%} of the total anion yield. The complex internal rearrangement processes triggered by electron transfer to acetic acid have been evaluated with the help of theoretical calculations at the DFT levels explaining the fragmentation channel yielding OH-.

Hoshino, M., P. Limão-Vieira, A. Suga, H. Kato, F. {Ferreira Da Silva}, F. Blanco, G. García, and H. Tanaka. "{Crossed-beam experiment for the scattering of low- and intermediate-energy electrons from BF3: A comparative study with XF3 (X = C, N, and CH) molecules}." Journal of Chemical Physics. 143 (2015). Abstract

© 2015 AIP Publishing LLC.Absolute differential cross sections (DCSs) for electron interaction with BF{\textless}inf{\textgreater}3{\textless}/inf{\textgreater} molecules have been measured in the impact energy range of 1.5-200 eV and recorded over a scattering angle range of 15°-150°. These angular distributions have been normalized by reference to the elastic DCSs of the He atom and integrated by employing a modified phase shift analysis procedure to generate integral cross sections (ICSs) and momentum transfer cross sections (MTCSs). The calculations of DCSs and ICSs have been carried out using an independent atom model under the screening corrected additivity rule (IAM-SCAR). The present elastic DCSs have been found to agree well with the results of IAM-SCAR calculation above 20 eV, and also with a recent Schwinger multichannel calculation below 30 eV. Furthermore, in the comparison with the XF{\textless}inf{\textgreater}3{\textless}/inf{\textgreater} (X = B, C, N, and CH) molecules, the elastic DCSs reveal a similar angular distribution which are approximately equal in magnitude from 30 to 200 eV. This feature suggests that the elastic scattering is dominated virtually by the 3-outer fluorine atoms surrounding the XF{\textless}inf{\textgreater}3{\textless}/inf{\textgreater} molecules. The vibrational DCSs have also been obtained in the energy range of 1.5-15 eV and vibrational analysis based on the angular correlation theory has been carried out to explain the nature of the shape resonances. Limited experiments on vibrational inelastic scattering confirmed the existence of a shape resonance with a peak at 3.8 eV, which is also observed in the vibrational ICS. Finally, the estimated elastic ICSs, MTCSs, as well as total cross sections are compared with the previous cross section data available.

Neustetter, Michael, Julia Aysina, Filipe Ferreira da Silva, and Stephan Denifl. "{DEA to bare and water-solvated pyrimidine clusters}." XXIX INTERNATIONAL CONFERENCE ON PHOTONIC, ELECTRONIC, AND ATOMIC COLLISIONS (ICPEAC2015), PTS 1-12. Eds. C. {Diaz, I. Rabadan, G. Garcia, L. Mendez, and F. } Martin. Vol. 635. Journal of Physics Conference Series, 635. Univ Autonoma Madrid; Consejo Super Investigaciones Cient, 2015. Abstract

In the present work we investigate the interaction of low energetic electrons with biologically relevant molecules. Our aim is to observe differences in the fragmentation pattern in the case of isolated molecules, bare clusters and water-solvated clusters. In this context we present the first results regarding electron attachment to nano-solvated biomolecule clusters.

Ribar, A., M. Danko, J. Országh, F. {Ferreira Da Silva}, I. Utke, and Š. Matejčík. "{Dissociative excitation study of iron pentacarbonyl molecule Topical Issue: Elementary Processes with Atoms and Molecules in Isolated and Aggregated States Friedrich Aumayr, Bratislav Marinkovic, Štefan Matejčík, John Tanis, Kurt H. Becker}." European Physical Journal D. 69 (2015). Abstract

© 2015 EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg.The processes of dissociative excitation (DE) and dissociative ionisation with excitation (DIE) of iron pentacarbonyl, Fe(CO){\textless}inf{\textgreater}5{\textless}/inf{\textgreater}, have been studied using a crossed electron-molecule beam experimental apparatus (Electron Induced Fluorescence Apparatus, EIFA). Using EIFA we were able to record the emission spectrum of the molecule in the UV-VIS range, as well as the photon efficiency curves initiated by electron impact. The emission spectrum of Fe(CO){\textless}inf{\textgreater}5{\textless}/inf{\textgreater} initiated by impact of 50 eV electrons was recorded in the spectral range between 200 nm and 470 nm. It shows a high density of emission lines and bands (mainly iron lines and carbonyl bands). Additionally, we have measured photon efficiency curves (PECs) as a function of the electron impact energy for several lines and bands. On the basis of the PECs we have discussed the reaction mechanism and the energetics of the reactions associated with the DE and DIE processes.

Lange, E., G. Meneses, T. Cunha, J. Krasuska, J. Kopyra, G. Garcia, F. da Silva, and P. Limao-Vieira. "{Electron induced fragmentation of sulphur containing biological prototypes: thiaproline and taurine}." XXIX INTERNATIONAL CONFERENCE ON PHOTONIC, ELECTRONIC, AND ATOMIC COLLISIONS (ICPEAC2015), PTS 1-12. Eds. C. {Diaz, I. Rabadan, G. Garcia, L. Mendez, and F. } Martin. Vol. 635. Journal of Physics Conference Series, 635. Univ Autonoma Madrid; Consejo Super Investigaciones Cient, 2015. Abstract

Here we present negative ion formation driven by electron transfer in atom (potassium) molecule collision and dissociative electron attachment in sulphur containing compounds, probing the influence of sulphur atoms in the decomposition mechanism of two biological relevant molecules: thiaproline and taurine.

Blanco, F., A. Munoz, D. Almeida, F. da Silva, P. Limao-Vieira, A. Verkhovtsev, L. Ellis-Gibbings, K. Krupa, A. Traore, and G. Garcia. "{Modeling secondary particle tracks generated by high-energy protons in water}." XXIX INTERNATIONAL CONFERENCE ON PHOTONIC, ELECTRONIC, AND ATOMIC COLLISIONS (ICPEAC2015), PTS 1-12. Eds. C. {Diaz, I. Rabadan, G. Garcia, L. Mendez, and F. } Martin. Vol. 635. Journal of Physics Conference Series, 635. Univ Autonoma Madrid; Consejo Super Investigaciones Cient, 2015. Abstract

We present interaction probability data of low-energy secondary electrons and positrons produced due to the proton impact. The probability distribution functions serve as input data for the Low Energy Particle Track Simulation (LEPTS) approach which allows one to include the effect of low-energy species in medical applications of radiation and in ion-beam cancer therapy, in particular.

Neustetter, Michael, Julia Aysina, Filipe {Ferreira da Silva}, and Stephan Denifl. "{The Effect of Solvation on Electron Attachment to Pure and Hydrated Pyrimidine Clusters}." Angewandte Chemie International Edition. 54 (2015): 9124-9126. AbstractWebsite
n/a
2014
{Ferreira Da Silva}, F., J. Rafael, T. Cunha, D. Almeida, and P. Limão-Vieira. "{Electron transfer to aliphatic amino acids in neutral potassium collisions}." International Journal of Mass Spectrometry. 365-366 (2014): 238-242. AbstractWebsite
n/a
Almeida, D., F. da Silva, S. Eden, G. Garcia, and P. Limao-Vieira. "{New Fragmentation Pathways in K-THF Collisions As Studied by Electron-Transfer Experiments: Negative Ion Formation}." JOURNAL OF PHYSICAL CHEMISTRY A. 118 (2014): 690-696. AbstractWebsite

Time-of-flight (TOF) negative ion mass spectra have been obtained in collisions of 20-100 eV neutral potassium atoms with tetrahydrofuran (C4H8O), an analogue for the sugar unit in DNA/RNA. Major enhancements in O- and C2H3O- production were observed compared with earlier dissociative electron attachment (DEA) experiments. In further contrast with DEA, no evidence was observed for dehydrogenated parent anions, and three new fragment anions were detected: CH-, C-2(-), and C2H-. These contrasting results for potassium impact and DEA highlight significant differences in the reaction pathways initiated by the two electron delivery processes.

Almeida, D., M. - C. Bacchus-Montabonel, F. da Silva, G. Garcia, and P. Limao-Vieira. "{Potassium-Uracil/Thymine Ring Cleavage Enhancement As Studied in Electron Transfer Experiments and Theoretical Calculations}." JOURNAL OF PHYSICAL CHEMISTRY A. 118 (2014): 6547-6552. Abstract

We report experimental and theoretical studies on ring cleavage enhancement in collisions of potassium atoms with uracil/thymine to further increase the understanding of the complex mechanisms yielding such fragmentation pathways. In these electron transfer processes time-of-flight (TOP) negative ion mass spectra were obtained in the collision energy range 13.5-23.0 eV. We note that CNO- is the major ring breaking anion formed and its threshold formation is discussed within the collision energy range studied. Such a decomposition process is supported by the first theoretical calculations to clarify how DNA/RNA pyrimidine base fragmentation is enhanced in electron transfer processes yielding ion-pair formation.

Almeida, D., Ferreira F. da Silva, J. Kopyra, G. Garcia, and P. Limao-Vieira. "{Anion formation in gas-phase potassium-uridine collisions}." INTERNATIONAL JOURNAL OF MASS SPECTROMETRY. 365 (2014): 243-247. AbstractWebsite

In this study we report negative ion fragmentation patterns obtained from time-of-flight (TOF) mass spectrometry in potassium-uridine collisions at 30, 70 and 100 eV. The dominant fragments from uridine are also the most abundant from the individual units in potassium collisions with uracil, tetrahydrofuran (THF) and D-ribose. We observe no dehydrogenated parent anion formation. Special emphasis is given to the dissociation mechanisms lending support to the breaking of the N-glycosidic bond as an initial step in the fragmentation of the transient negative ion (TNI). Within their role as sugar unit surrogates, THF and D-ribose (DR) provide useful information for the study of uridine, and presumably other nucleosides from the point of view of DNA/RNA subunits integrity in the biological environment. (C) 2014 Elsevier B.V. All rights reserved.

da Silva, F., D. Almeida, G. Garcia, and P. Limao-Vieira. "{CNO- formation through selective bond cleavage}." XXVIII INTERNATIONAL CONFERENCE ON PHOTONIC, ELECTRONIC AND ATOMIC COLLISIONS (ICPEAC). Vol. 488. Journal of Physics Conference Series, 488. Natl Nat Sci Fdn China; Chinese Acad Sci; Int Union Pure {&} Appl Phys; Inst Modern Phys; Youth Innovat Promot Assoc, Inst Modern Phys, 2014. Abstract

H- and CNO- site and bond selectivity formation is shown in the context of atom-molecule collisions.

Hoshino, M., P. Limao-Vieira, K. Anzai, H. Kato, H. Cho, D. Mogi, T. Tanioka, F. da Silva, D. Almeida, F. Blanco, G. Garcia, O. Ingolfsson, and H. Tanaka. "{Elastic differential cross sections for C4F6 isomers in the 1.5-200 eV energy electron impact: Similarities with six fluorine containing molecules and evidence of F-atom like scattering}." JOURNAL OF CHEMICAL PHYSICS. 141 (2014). AbstractWebsite

We report absolute elastic differential cross sections for electron interactions with the C4F6 isomers, hexafluoro-1,3-butadiene (1,3-C4F6), hexafluoro-2-butyne (2-C4F6), and hexafluorocyclobutene (c-C4F6). The incident electron energy range is 1.5-200 eV, and the scattered electron angular range for the differential measurements varies from 15 degrees to 150 degrees. In all cases the absolute scale of the differential cross section was set using the relative flow technique, with helium as the reference species. Atomic-like behaviour in these scattering systems is shown here for the first time, and is further investigated by comparing the elastic cross sections for the C4F6 isomers with other fluorinated molecules, such as SF6 and CnF6 (n = 2, 3, and 6). We note that for all the six-F containing molecules, the scattering process for electron energies above 30 eV is indistinguishable. Finally, we report results for calculations of elastic differential cross sections for electron scattering from each of these isomers, within an optical potential method and assuming a screened corrected independent atom representation. The level of agreement between these calculations and our measurements is found to be quite remarkable in all cases. (C) 2014 AIP Publishing LLC.