Applications of the Schwinger Multichannel method with pseudopotentials to electron scattering from polyatomic molecules II: rotational excitation cross sections

This paper reports results for rotational excitation of H2O and H2S molecules by electron impact. It is also a databasis including tables of previously published rotationally resolved cross sections for CH4, SiH4, GeH4, SnH4, PbH4, NH3, PH3, AsH3, SbH3, CF4, CCl4, SiCl4 SiBr4, and SiI4. Our scattering amplitudes were calculated using the Schwinger multichannel method with norm-conserving pseudopotentials and the rotational resolved cross sections were obtained with the help of the adiabatic nuclei rotation approximation. Our results are in good agreement with other theoretical data and experimental results when available.2129Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Electron and positron scattering from 1,1-C₂H₂F₂

1,1-difluoroethylene (1,1-C₂H₂F₂) molecules have been studied for the first time experimentally and theoretically by electron and positron impact. 0.4-1000 eV electron and 0.2-1000 eV positron impact total cross sections (TCSs) were measured using a retarding potential time-of-flight apparatus. In order to probe the resonances observed in the electron TCSs, a crossed-beam method was used to investigate vibrational excitation cross sections over the energy range of 1.3-49 eV and scattering angles 90 degrees and 120 degrees for the two loss energies 0.115 and 0.381 eV corresponding to the dominant C-H (ν₂ and ν₉) stretching and the combined C-F (ν₃) stretching and CH₂ (ν₁₁) rocking vibrations, respectively. Electron impact elastic integral cross sections are also reported for calculations carried out using the Schwinger multichannel method with pseudopotentials for the energy range from 0.5 to 50 eV in the static-exchange approximation and from 0.5 to 20 eV in the static-exchange plus polarization approximation. Resonance peaks observed centered at about 2.3, 6.5, and 16 eV in the TCSs have been shown to be mainly due to the vibrational and elastic channels, and assigned to the B₂, B₁, and A₁ symmetries, respectively. The pi* resonance peak at 1.8 eV in C₂H₄ is observed shifted to 2.3 eV in 1,1-C₂H₂F₂ and to 2.5 eV in C₂F₄; a phenomenon attributed to the decreasing C=C bond length from C₂H₄ to C₂F₄. For positron impact a conspicuous peak is observed below the positronium formation threshold at about 1 eV, and other less pronounced ones centered at about 5 and 20 eV.The work was supported in part by a Grant-in-Aid, the Ministry of Education, Science, Technology, Sport and Culture, Japan, the Japan Society for the Promotion of Science JSPS, and the Japan Atomic Energy Research Institute JAERI. One of the authors C.M. is also grateful to the JSPS for financial support under Grant No. P04064. Another author H.T. acknowledges Dr. T. Ozeki of the JAERI for his encouragement and support during this work. This work was also done under the International Atomic Energy Agency IAEA project for three of the authors C.M., M.H., and H.T.. Two of the authors M.H.F.B. and M.A.P.L. acknowledge support from the Brazilian agency Conselho Nacional de Desenvolvimento Científico e Tecnológico CNPq. MHFB also acknowledges support from the Paraná state agency Fundação Araucária and from FINEP ( under Project No. CT-Infra 1)

Recent advances in the application of the Schwinger multichannel method with pseudopotentials to electron-molecule collisions

The Schwinger multichannel method [K. Takatsuka and V. McKoy, Phys. Rev. A 30, 1734 (1984)], which is based on the Schwinger variational principle for the scattering amplitude [J. Schwinger, Phys. Rev. 72, 742 (1947)], was designed to account for exchange, polarization and electronically multichannel coupling effects in the low-energy region of electron scattering from molecules with arbitrary geometry. The applications of the method became more ambitious with the availability of computer power combined with parallel processing, use of norm-conserving pseudopotentials and improvement of the description of target excited states (minimal orbital basis for single configuration interaction). The most recent applications involving 33 and 45 electronically open channels for phenol and ethylene molecules, represent good examples of the present status of the method. In this colloquium, we review the strategy and point out new directions to apply the method in its full extension

Combining proton or photon irradiation with epothilone B : An in vitro study of cytotoxicity in human cancer cells

Recently, the use of proton beams in cancer therapy is becoming widespread, and tumour treatment modalities combining radiosensitizing chemical agents with irradiation are under investigation in order to achieve greater tumour local control and reduce the probability of distant failures. The combined treatment modality of radiation and the clinically relevant microtubule-stabilizing compound epothilone B is a promising approach for anticancer therapy. In the present study, we investigated the cytotoxicity of a spread out Bragg peak (SOBP) proton beam, as well as of 6 MV photons, in human glioblastoma (U251 MG) and lung adenocarcinoma (A549) cells pretreated for 24 h, or not, with epothilone B at concentrations of 0.125 and 0.075 nM respectively. Proton irradiation was performed at the middle position of an actively modulated SOBP (12\u201318 cm depth in water) and cell survival was evaluated by a colony forming assay. For both cell lines, survival curves after proton or photon irradiation alone showed linear quadratic behaviour with proton RBE (relative biological effectiveness), compared with photons at 10% survival, of 1.5 \ub1 0.2. Treatment of cells with epothilone B at subnanomolar concentration has an anticlonogenic effect. Furthermore, differently from the results found with radiation alone, the survival curves for the combined treatment epothilone B\u2013radiation showed a linear trend and analysis of the interaction of the two cytotoxic agents indicated a slight synergism. These data provide a radiobiological basis for further experiments, as well as clinical studies

Tamoxifen reduces plasma homocysteine levels in healthy women.

Treatment with tamoxifen is associated with reduced incidence of myocardial infarction. As plasma homocysteine is an independent risk factor for cardiovascular disease, we studied the effects of tamoxifen on plasma homocysteine in 66 healthy women participating in the Italian prevention trial of breast cancer who were randomized in a double-blind manner to tamoxifen 20 mg day(-1) or placebo for 5 years. They were aged between 35 and 70 years, had undergone previous hysterectomy for non-malignant conditions and had no contraindications to the use of tamoxifen. Plasma levels of total homocysteine (tHcy) were measured at randomization and after 2 and 6 months. The mean +/- s.d. plasma levels of tHcy were 7.59 +/- 1.71 micromol l(-1), 7.25 +/- 1.61 and 7.09 +/- 1.33 in the tamoxifen group and 8.07 +/- 2.06, 7.93 +/- 1.77 and 8.12 +/- 2.04 in the placebo group at 0, 2 and 6 months (P = 0.008 for the between-group difference over time). The higher the baseline tHcy level, the greater was the lowering effect of tamoxifen. No statistically significant effect of age, body mass index or smoking habit on baseline tHcy levels and its variation over time was found. In conclusion, tamoxifen (20 mg day(-1) for 6 months) decreased plasma tHcy levels in healthy women. This effect may contribute to its protective effect on myocardial infarction

Positron scattering from formic acid

We report on measurements of total cross sections for positron scattering from the fundamental molecule formic acid (HCOOH). In this case, the energy range of our experimental work is 0.3-50.2 eV. Our interpretation of these data was somewhat complicated by the fact that at room temperature, formic acid vapor consists of about 95% monomer and 5% dimer forms, so that the present cross sections represent an average for that ensemble. To assist us in interpreting the data, rigorous Schwinger multichannel level calculations for positron elastic scattering from the formic acid monomer were also undertaken. These calculations, incorporating an accurate model for the target polarization, are found to be in good qualitative agreement with our measured data, particularly when allowance is made for the target beam mixture (monomer versus dimer) in the experiment

Valence and Rydberg excitations of 2-fluorotoluene in the 4.4–10.8 eV photoabsorption energy region

Funding Information: PASR acknowledges support from the Brazilian agency Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES). ASB and MHFB acknowledge support from the Brazilian agency Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq). PASR, ASB and MHFB also acknowledge Prof. Carlos de Carvalho for computational support at LFTC-DFis-UFPR and at LCPAD-UFPR. The authors wish to acknowledge the beam time at the ISA synchrotron, Aarhus University, Denmark. The research leading to this result has been supported by the project CALIPSOplus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020. SK, AIL and PLV acknowledges the Portuguese National Funding Agency (FCT) through research grant CEFITEC (UIDB/00068/2020) . PLV also acknowledges his visiting professor position at Federal University of Paraná, Curitiba, Brazil. This contribution is also based upon work from the COST Action CA18212-Molecular Dynamics in the GAS phase (MD-GAS), supported by COST (European Cooperation in Science and Technology). Funding Information: PASR acknowledges support from the Brazilian agency Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES). ASB and MHFB acknowledge support from the Brazilian agency Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq). PASR, ASB and MHFB also acknowledge Prof. Carlos de Carvalho for computational support at LFTC-DFis-UFPR and at LCPAD-UFPR. The authors wish to acknowledge the beam time at the ISA synchrotron, Aarhus University, Denmark. The research leading to this result has been supported by the project CALIPSOplus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020. SK, AIL and PLV acknowledges the Portuguese National Funding Agency (FCT) through research grant CEFITEC (UIDB/00068/2020). PLV also acknowledges his visiting professor position at Federal University of Paraná, Curitiba, Brazil. This contribution is also based upon work from the COST Action CA18212-Molecular Dynamics in the GAS phase (MD-GAS), supported by COST (European Cooperation in Science and Technology). Publisher Copyright: © 2023 The Author(s)The electronic state spectroscopy of 2-fluorotoluene in the gas phase has been investigated for the first time using high-resolution vacuum ultraviolet photoabsorption experiments in the 4.4–10.8 eV energy-range, with absolute cross-section measurements obtained. Additionally, we also present a novel set of ab initio calculations (vertical excitation energies and oscillator strengths) at two different levels of theory, equation-of-motion coupled-cluster singles and doubles (EOM-CCSD) and time-dependent density functional theory (TD-DFT). These are used in the assignment of valence, mix valence-Rydberg and Rydberg transitions, with the associated vibronic series analysed. The measured absolute photoabsorption cross-sections have been used to calculate the photolysis lifetime of 2-fluorotoluene in the Earth's atmosphere.publishersversionpublishe

Positron collisions with ethene

We present experimental and theoretical cross sections for positron collisions with ethene molecules. The experimental total cross sections (TCSs) were obtained with a linear transmission technique, for energies from 0.1 eV up to 70 eV. The calculations employed the Schwinger multichannel method and were performed in the static plus polarization approximation for energies up to 10 eV. Our calculated elastic cross sections indicate a Ramsauer-Townsend minimum around 2.8 eV and a virtual state, in agreement with previous calculations by da Silva et al. [ Phys. Rev. Lett. 77 1028 (1996)]. We found reasonable agreement between the calculated elastic integral cross section and the measured total cross section below the positronium formation threshold. The present results are also in quite good agreement with available theoretical and experimental data, although for the experiments this is only true for TCSs above about 7 eV

Theoretical and experimental study on electron interactions with chlorobenzene: Shape resonances and differential cross sections

9 págs.; 6 figs.; 1 tab.In this work, we report theoretical and experimental cross sections for elastic scattering of electrons by chlorobenzene (ClB). The theoretical integral and differential cross sections (DCSs) were obtained with the Schwinger multichannel method implemented with pseudopotentials (SMCPP) and the independent atom method with screening corrected additivity rule (IAM-SCAR). The calculations with the SMCPP method were done in the static-exchange (SE) approximation, for energies above 12 eV, and in the static-exchange plus polarization approximation, for energies up to 12 eV. The calculations with the IAM-SCAR method covered energies up to 500 eV. The experimental differential cross sections were obtained in the high resolution electron energy loss spectrometer VG-SEELS 400, in Lisbon, for electron energies from 8.0 eV to 50 eV and angular range from 7 to 110. From the present theoretical integral cross section (ICS) we discuss the low-energy shape-resonances present in chlorobenzene and compare our computed resonance spectra with available electron transmission spectroscopy data present in the literature. Since there is no other work in the literature reporting differential cross sections for this molecule, we compare our theoretical and experimental DCSs with experimental data available for the parent molecule benzene. Published by AIP Publishing.A.S.B., M.T.N.V., S.d’A.S., and M.H.F.B. acknowledge the Brazilian Agency Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), under CAPES/FCT Programme (Process No. 23038.002465/2014-87). M.T.N.V., S.d’A.S., and M.H.F.B. acknowledge support from the Brazilian Agency Conselho Nacional de Desenvolvimento Científico e Tecnológico. M.H.F.B. acknowledges support from Finep (under project CT-Infra), and M.T.N.V. from São Paulo Research Foundation (FAPESP). A.S.B., S.d’A.S., and M.H.F.B. acknowledge computational support from Professor Carlos M. de Carvalho at LFTC-DFis-UFPR and at LCPADUFPR and from CENAPAD-SP. F.F.S. acknowledges the Portuguese National Funding Agency FCT through researcher Contract No. IF-FCT IF/00380/2014 and together with P.LV. the research Grant No. UID/FIS/00068/2013. F.B. and G.G. acknowledge partial financial support from the Spanish Ministry MINECO (Project No. FIS2012-31230).Peer Reviewe

Communication: Transient Anion States Of Phenol…(h₂o)n (n = 1, 2) Complexes: Search For Microsolvation Signatures.

We report on the shape resonance spectra of phenol-water clusters, as obtained from elastic electron scattering calculations. Our results, along with virtual orbital analysis, indicate that the well-known indirect mechanism for hydrogen elimination in the gas phase is significantly impacted on by microsolvation, due to the competition between vibronic couplings on the solute and solvent molecules. This fact suggests how relevant the solvation effects could be for the electron-driven damage of biomolecules and the biomass delignification [E. M. de Oliveira et al., Phys. Rev. A 86, 020701(R) (2012)]. We also discuss microsolvation signatures in the differential cross sections that could help to identify the solvated complexes and access the composition of gaseous admixtures of these species.14105110