Ionisation of PF3: absolute partial electron ionisation cross sections and the formation and reactivity of dication states

Absolute partial electron ionisation cross sections, and precursor-specific partial electron ionisation cross sections, for the formation of cations from phosphorus trifluoride (PF3) are reported over the electron energy range 50-200 eV. The absolute values are determined by the measurement of cross sections relative to the formation of PF3+ using 2D ion-ion coincidence time-of-flight mass spectrometry and subsequent scaling using binary encounter-Bethe calculations of the total ionisation cross section. This new dataset significantly augments the partial ionisation cross sections for electron ionization PF3 found in literature, addressing previous discrepancies in the branching ratios of product ions, and provides the first values for the precursor-specific cross sections. Comparisons to calculated cross sections from the literature are encouraging, although there are discrepancies for individual ions. The coincidence experiments indicate that double and triple ionisation generate approximately 20 % of the cationic ionisation products at 200 eV electron energy. One dissociative dication state, dissociating to PF2+ + F+, is clearly identified as the lowest triplet state of PF32+ and five different dications (PF32+, PF22+, PF2+, P2+ and F2+) are detected in the mass spectra. The dication energetics revealed by the experiments are supported by a computational investigation of the dication’s electronic structure. The cross sections reported will allow more accurate modelling of the role of the ionization of PF3 in energetic environments. A first investigation of the bimolecular reactivity of metastable states of PF32+ is also reported. In collisions with Ar, O2 and CO dissociative single electron transfer dominates the product ion yield, whereas collision-induced dissociation of the dication is important following collisions with Ne. Consideration of the energetics of these processes indicates the reactant dication beam contains ions in both the ground singlet state and the first excited triplet state. The deduction regarding the longevity of the triplet state is supported by metastable signals in the coincidence spectra. Weak signals corresponding to the formation of ArF+ are detected following PF32+ collisions with Ar, and experimental and computational considerations indicate this new chemical bond is formed via a collision complex

Novel experimental setup for time-of-flight mass spectrometry ion detection in collisions of anionic species with neutral gas-phase molecular targets

8 págs.; 4 figs.; Open Access funded by Creative Commons Atribution Licence 4.0We 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 O2 precursor projectile, where we show clear evidence of O– and O2 – 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 –.PLV acknowledges the Portuguese Foundation for Science and Technology (FCT-MEC) through SFRH/BSAB/105792/ 2014 during his sabbatical stay at CSIC, Madrid and the research grants PTDC/FIS-ATO/1832/2012 and UID/FIS/00068/ 2013. FFS acknowledges FCT-MEC through researcher grant IF-FCT IF/00380/2014. We also acknowledge the Spanish Ministerio de Economía y Competitividad (Project No. FIS 2012-31230). Some of this work forms part of the EU/ESF COST Actions CM1401 and CM1301, Our Astro-Chemical History and Chemistry for Electron-Induced Nanofabrication, respectively. LE-G and GG acknowledge the FP7-PEOPLE-2013-ITN research grant “Advanced Radiotherapy, Generated by Exploiting Nanoprocesses and Technologies (ARGENT)”.Peer Reviewe

New process to describe radiation damage at the molecular level. Application to I-125 seeds in water

ICPEAC 2015, Toledo, Spain on 22 –28 July 2015; http://www.icpeac2015.com/We present the first step of a general study on induced damage by 125I in water at the molecular level. Requirements for such a study are introduced and preliminary results on the emission spectra of 125I seeds are presented.This work was supported by MINECO (FIS2012-31230) and FCT/MEC, RaBBiT, PD-F,PD/00193/2012); UID/Multi/04378/2013 (UCIBIO); UID/FIS/00068/2013 (CEFITEC); and grant number SFRH/BD/52536/2014.Peer Reviewe

Intermediate energy cross sections for electron-impact vibrational-excitation of pyrimidine

We report differential cross sections (DCSs) and integral cross sections (ICSs) for electron-impact vibrational-excitation of pyrimidine, at incident electron energies in the range 15–50 eV. The scattered electron angular range for the DCS measurements was 15°–90°. The measurements at the DCS-level are the first to be reported for vibrational-excitation in pyrimidine via electron impact, while for the ICS we extend the results from the only previous condensed-phase study [P. L. Levesque, M. Michaud, and L. Sanche, J. Chem. Phys. 122, 094701 (2005)], for electron energies ⩽12 eV, to higher energies. Interestingly, the trend in the magnitude of the lower energy condensed-phase ICSs is much smaller when compared to the corresponding gas phase results. As there is no evidence for the existence of any shape-resonances, in the available pyrimidine total cross sections [Baek et al., Phys. Rev. A 88, 032702 (2013); Fuss et al., ibid. 88, 042702 (2013)], between 10 and 20 eV, this mismatch in absolute magnitude between the condensed-phase and gas-phase ICSs might be indicative for collective-behaviour effects in the condensed-phase results

The role of pyrimidine and water as underlying molecular constituents for describing radiation damage in living tissue: A comparative study

8 págs.; 7 figs.; 2 tabs.© 2015 AIP Publishing LLC. Water is often used as the medium for characterizing the effects of radiation on living tissue. However, in this study, charged-particle track simulations are employed to quantify the induced physicochemical and potential biological implications when a primary ionising particle with energy 10 keV strikes a medium made up entirely of water or pyrimidine. Note that pyrimidine was chosen as the DNA/RNA bases cytosine, thymine, and uracil can be considered pyrimidine derivatives. This study aims to assess the influence of the choice of medium on the charged-particle transport, and identify how appropriate it is to use water as the default medium to describe the effects of ionising radiation on living tissue. Based on the respective electron interaction cross sections, we provide a model, which allows the study of radiation effects not only in terms of energy deposition (absorbed dose and stopping power) but also in terms of the number of induced molecular processes. Results of these parameters for water and pyrimidine are presented and compared.This research was supported by the Australian Research Council (ARC) through its Centres of Excellence Program. D.B.J. thanks the ARC for provision of a Discovery Early Career Researcher Award. We also acknowledge the support of the Spanish Ministerio de Economia y Competitivad under Project No. FIS 2012-31230 and the European Union COST Actions (MP1002 and CM1301). P.L.V. acknowledges the Portuguese Foundation for Science and Technology (FCTMEC) through research grants PTDC/FIS-ATO/1832/2012, UID/FIS/00068/2013, and SFRH/BSAB/105792/2014. P.L.V. also acknowledges his Visiting Professor position at Flinders University, Adelaide, South Australia.Peer Reviewe

Induced molecular dissociations as a radiation damage descriptor: nanodosimetry

Conferencia invitada; IBER 2015, 6-9th September, Aveiro – Portugal; http://iber2015.web.ua.pt/Traditional dosimetry is based on the proportionality between the energy absorbed by the medium (absorbed dose) and the induced damage. This assumption applies for relatively high irradiated volumes and requires some equilibrium conditions. However, for small volumes being relatively far from the central irradiated areas these conditions are not observed and radiation damage is mainly driven by low energy secondary species (electrons and radicals) which induce molecular dissociations via electronic and vibrational excitations, electron attachment and chemical reactions. We will present here an integrated modelling procedure to simulate particle radiation tracks including those of all generated secondary species and their further interactions with the molecular constituent of the medium. For any selected volume of interest, this model provides not only the total energy transferred to that area but also the number and type of interactions taking place in it [1].Peer Reviewe

Modelling secondary particle tracks generated by high-energy protons in water

1 pág.; XXIX International Conference on Photonic, Electronic, and Atomic Collisions (ICPEAC2015); Open Access funded by Creative Commons Atribution Licence 3.0We 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.This work has been supported by the Spanish Ministry of Economía y Productividad (Project FIS2012-31320). We also acknowledge partial funding from the Portuguese Foundation for Science and Technology (FCT-MCTES), research grant PEstOE/FIS/UI0068/2011,the EU/ESF COST Actions Nano-IBCT - MP1002 and CELINA CM- 1301, and from the FP7 Multi-ITN Project ”Advanced Radiotherapy, Generated by Exploiting Nanoprocesses and Technologies” (ARGENT) (Grant Agreement n◦608163).Peer Reviewe

Modeling secondary particle tracks generated by high-energy protons in water

ICPEAC 2015, Toledo, Spain on 22 –28 July 2015; http://www.icpeac2015.com/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.his work has been supported by the Spanish Ministry of Economía y Productividad (Project FIS2012-31320). We also acknowledge partial funding from the Portuguese Foundation for Science and Technology (FCT-MCTES), research grant PEstOE/FIS/UI0068/2011,the EU/ESF COST Actions Nano-IBCT - MP1002 and CELINA CM- 1301, and from the FP7 Multi-ITN Project ”Advanced Radiotherapy, Generated by Exploiting Nanoprocesses and Technologies” (ARGENT) (Grant Agreement n◦608163).Peer Reviewe

Positron scattering from pyridine

We present a range of cross section measurements for the low-energy scattering of positrons from pyridine, for incident positron energies of less than 20 eV, as well as the independent atom model with the screening corrected additivity rule including interference effects calculation, of positron scattering from pyridine, with dipole rotational excitations accounted for using the Born approximation. Comparisons are made between the experimental measurements and theoretical calculations. For the positronium formation cross section, we also compare with results from a recent empirical model. In general, quite good agreement is seen between the calculations and measurements although some discrepancies remain which may require further investigation. It is hoped that the present study will stimulate development of ab initio level theoretical methods to be applied to this important scattering system

Electron transport in furfural: dependence of the electron ranges on the cross sections and the energy loss distribution functions

GEC 2016 ; 69th Annual Gaseous Electronics Conference ; Bochum, Germany, Monday–Friday, October 10–14Recent theoretical and experimental studies have provided a complete set of differential and integral electron scattering cross section data from furfural over a broad energy range1, 2. The energy loss distribution functions have been determined in this study by averaging electron energy loss spectra for different incident energies and scattering angles. All these data have been used as input parameters for an event by event Monte Carlo simulation procedure to obtain the electron energy deposition patterns and electron ranges in liquid furfural. The dependence of these results on the input cross sections is then analysed to determine the uncertainty of the simulated values.Peer Reviewe