A study of electron scattering from benzene: excitation of the 1B1u, 3E2g, and 1E1u electronic states

We report results from measurements for differential and integral cross sections of the unresolved 1B1u and 3E2g electronic states and the 1E1u electronic state in benzene. The energy range of this work was 10–200 eV, while the angular range of the differential cross sections was -3°–130°. To the best of our knowledge there are no other corresponding theoretical or experimental data against which we can compare the present results. A generalized oscillator strength analysis was applied to our 100 and 200 eV differential cross section data, for both the 1B1u and 1E1u states, with optical oscillator strengths being derived in each case. The respective optical oscillator strengths were found to be consistent with many, but not all, of the earlier theoretical and experimental determinations. Finally, we present theoretical integral cross sections for both the 1B1u and 1E1u electronic states, as calculated within the BEf-scaling formalism, and compare them against relevant results from our measurements. From that comparison, an integral cross section for the optically forbidden 3E2g state is also derived

Electron excitation of the Schumann–Runge continuum, longest band, and second band electronic states in O2

We report measurements of differential and integral cross sections for electron excitation of the Schumann–Runge continuum, longest band, and second band electronic states in molecular oxygen. The energy range of the present study is 15–200 eV, with the angular range of the differential cross section (DCS) measurements from 2 to 130°. A generalized oscillator strength analysis is then employed in order to derive integral cross sections (ICSs) from the corresponding DCSs, and these ICSs are compared with relevant energy and oscillator strength scaled Born cross section results determined as a part of this investigation. Interestingly, while the present Schumann–Runge continuum and second band ICSs were in reasonable agreement with the respective BEf-scaling results, agreement for the longest band was poor below 100 eV with a possible reason for this apparently anomalous behavior being canvassed here. Finally, where possible all present data are compared with the results from earlier measurements and calculations with the level of agreement found being very good in some cases and marginal in others

A-band methyl halide dissociation via electronic curve crossing as studied by electron energy loss spectroscopy

Excitation of the A-band low-lying electronic states in the methyl halides, CH3I, CH3Br, CH3Cl, and CH3F, has been investigated for the (n→σ∗) transitions, using electron energy loss spectroscopy (EELS) in the range of 3.5–7.5 eV. For the methyl halides, CH3I, CH3Br, and CH3Cl, three components of the Q complex (3Q1, 3Q0, and 1Q1) were directly observed, with the exception of methyl fluoride, in the optically forbidden EELS experimental conditions of this investigation. The effect of electronic-state curve crossing emerged in the transition probabilities for the 3Q0 and 1Q1 states, with spin-orbit splitting observed and quantified against results from recent ab initio studies

Differential cross sections for the electron impact excitation of pyrimidine

We report on differential cross section (DCS) measurements for the electron-impact excitation of the electronic states of pyrimidine. The energy range of the present measurements was 15–50 eV with the angular range of the measurements being 10°–90°. All measured DCSs displayed forward-peaked angular distributions, consistent with the relatively large magnitudes for the dipole moment and dipole polarizability of pyrimidine. Excitations to triplet states were found to be particularly important in some energy loss features at the lower incident electron energies. To the best of our knowledge there are no other experimental data or theoretical computations against which we can compare the present results

Ion-pair formation in neutral potassium-neutral pyrimidine collisions: electron transfer experiments

We report novel data on ion-pair formation in hyperthermal (30-800 eV) neutral potassium collisions with neutral pyrimidine (Pyr, C4H4N2) molecules. In this collision regime, negative ions formed by electron transfer from the alkali atom to the target molecule were time-of-flight mass analyzed and the fragmentation patterns and branching ratios have been obtained. The most abundant product anions have been assigned to CN- and C2H- and the electron transfer mechanisms are comprehensively discussed. Particular importance is also given to the efficient loss of integrity of the pyrimidine ring in the presence of an extra electron, which is in contrast to dissociative electron attachment experiments yielding the dehydrogenated parent anion. Theoretical calculations were performed for pyrimidine in the presence of a potassium atom and provided a strong basis for the assignment of the lowest unoccupied molecular orbitals accessed in the collision process. In order to further our knowledge about the collision dynamics, potassium cation (K+) energy loss spectrum has been obtained and within this context, we also discuss the role of the accessible electronic states. A vertical electron affinity of (-5.69 ± 0.20) eV was obtained and may be assigned to a π∗3 (b 1) state that leads to CN- formation

The inotropic consequences of selective Na+/Ca2+ exchanger inhibition is controlled by the actual transport balance

The major goal of the cardiac Ca2+ handling is to control the actual magnitude and kinetics of the cell contractions and therefore contribute to the regulation of the cardiac output. The Na+/Ca2+ exchanger has a crucial role in the beat-to-beat Ca2+ balance by extruding a relatively small fraction of the released Ca2+. Since the exchanger works Ca2+ influx, as well as Ca2+ efflux mode in the same heart cycle, its inhibition theoretically could lead to Ca2+ loss or Ca2+ gain. The functional consequence of these effects could be manifested in negative inotropy which may have antiarrhythmic effects during Ca2+ overload, or could cause positive inotropy which is desired in heart failure. However the exact electrophysiological mechanism which determines these two outcomes is not clarified because of the lack of selective inhibitors. In this thesis we would like to address these issues by using novel, selective NCX compounds. The main results can be summarized as follows: 1) The novel NCX inhibitor GYKB-6635 effectively suppressed both mode of the NCX current measured by conventional ramp protocol. Our study showed the GYKB-6635 did not influence the kinetics of the L-type Ca2+ current and major K+-currents therefore it could be considered a promising experimental tool for future NCX research. 2) The selective NCX inhibition is able to cause both positive and negative inotropy by ORM-10962 in the cardiac cells, depending on the experimental condition. When the reverse mode is facilitated Ca2+ loss, in the case of forward mode enhancement Ca2+ gain occurs. The major underlying mechanism is the actual Ca2+ level of the sarcoplasmic reticulum which strongly depends on the function of the NCX. 3) The selective NCX inhibition by ORM-10962 reverts the hypokalaemia induced positive inotropy: the low [K+]o increases the intracellular Na+ level of the cells which shifts the actual reversal potential of the NCX facilitating reverse mode. The selective NCX inhibition may inhibit preferentially the reverse mode of the NCX under this setting which decreases the intracellular Ca2+ and cell shortening

Electron-scattering cross sections for collisions with tetrahydrofuran from 50 to 5000 eV

In this paper, we report on total electron tetrahydrofuran (C4H8O) scattering cross-section measurements for energies in the range from 50 to 5000 eV with experimental errors of about 5%. In addition, integral elastic and inelastic cross sections have been calculated over a broad energy range (1–10 000 eV), with an optical potential method assuming a screening-corrected independent atom representation. Partial and total ionization cross sections have been also obtained by combining simultaneous electron and ion measurements with a time-of-flight analysis of the ionic induced fragmentation. Finally, an average energy distribution of secondary electrons has been derived from these measurements in order to provide data for modeling electron-induced damage in biomolecular systems

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

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 degrees to 110 degrees. 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

Negative ion formation through dissociative electron attachment to the group IV tetrachlorides: Carbon tetrachloride, silicon tetrachloride and germanium tetrachloride

© 2018 Elsevier. This manuscript version is made available under the CC-BY-NC-ND 4.0 license:http://creativecommons.org/licenses/by-nc-nd/4.0/ This author accepted manuscript is made available following 24 month embargo from date of publication (Jan 2018) in accordance with the publisher’s archiving policyThe current contribution constitutes the third and final part of our trilogy of papers on electron attachment reactions of the group IV tetrahalides; XY4 (X = C, Si, Ge and Y = F, Cl, Br). In this context we extend our previous studies on XF4 and XBr4 and report results for electron attachment to the tetrachlorides: CCl4, SiCl4 and GeCl4 in the incident electron energy range from about 0 to 10 eV. At the same time we give a summary of the currently available literature on electron interactions with those latter compounds. Upon electron attachment the formation of Cl−, XCl3−, XCl2− and Cl2− is observed from all the tetrachlorides, and additionally the molecular anion SiCl4− is observed from SiCl4. The main DEA contributions are observed through narrow, threshold peaks (at 0 eV) and we attribute these features to single particle resonances associated with the a1 symmetry LUMOs of those compounds. Contributions from another low-lying resonance, which we assign as a 2T2 shape resonance associated with the t2 symmetry LUMO+1, is also observed in the ion yield curves for all the tetrachlorides. The energy of the peak position of those contributions varies in the range from about 1 to 2 eV, depending on the compound and the fragment formed. In addition to these low energy contributions, higher energy, fairly broad, features are observed for all the tetrachlorides. These contributions exhibit a peak in the energy range between 5 and 8 eV, again depending on the compound and the fragment formed. Further to the experimental data, we report DFT and coupled cluster calculations on the thermochemical thresholds for the individual fragments as well as the respective bond dissociation energies and electron affinities. These calculated values are compared with the experimental appearance energies and literature values, where they are available

UV/Vis+ Photochemistry Database : Structure, Content and Applications

Acknowledgments This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. However, the authors are indebted to those colleagues who support us in maintaining the database through the provision of spectral and other photochemical data and information. The National Center for Atmospheric Research is operated by the University Coporation for Atmopsheric Research, under the sponsorship of the National Science Foundation. Disclaimer: The views expressed in this paper are those of the authors and do not necessarily represent the views or policies of the U.S.EPA. Mention of trade names or products does not convey and should not be interpreted as conveying official U.S. EPA approval, endorsement, or recommendation.Peer reviewedPublisher PD