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The interaction between electrons and methane is studied with a particular focus on describing the dynamics of elastic and electronic excitation processes under the influence of the multichannel coupling effects. Elastic and electronically inelastic integral and differential cross sections are reported. These cross sections were calculated with the Schwinger multichannel method implemented with norm-conserving pseudopotentials within the minimal orbital basis for single-configuration interaction approach with up to 181 open channels. While an excellent agreement with previously published data is found in the elastic channel, the comparisons involving electronic excitation cross sections reveal significant discrepancies. Furthermore, the lack of reliable experimental data regarding the electronically inelastic channels hampers a more detailed analysis of the theoretical results. Additionally, total ionization and total cross sections for electron collisions with methane are also presented. By highlighting the current theoretical challenges in dealing with electron-induced electronic excitation of molecules, we seek to contribute to a deeper understanding of this scattering process and, thus, pave the way for future research. [ABSTRACT FROM AUTHOR]

Differential and integral cross sections for elastic and electronically inelastic scattering of electrons by the thiophene molecule were determined by means of the Schwinger multichannel method within the static-exchange plus polarization approximation in the energy range from 3.41 to 50 eV. We investigated the influence of multichannel coupling effects by calculating the cross sections according to different schemes of channel coupling that range from 1 to 61 open channels along with polarization effects, depending on the energy considered. The comparison of these results shows that the inclusion of more channels in the scattering calculations leads to a significant decrease in the magnitude of the cross sections. Present results corresponding to our best level of channel coupling at a given energy, both for elastic and electronically inelastic electron scattering by thiophene, display an overall good agreement with the data available in the literature. [ABSTRACT FROM AUTHOR]

This paper presents a joint experimental and theoretical study of positron scattering from furan. Experimental data were measured using the low energy positron beamline located at the Australian National University and cover an energy range from 1 eV to 30 eV. Cross sections were measured for total scattering, total elastic and inelastic scattering, positronium formation, and differential elastic scattering. Two theoretical approaches are presented: the Schwinger multichannel method and the independent atom method with screening corrected additivity rule. In addition, our data are compared to corresponding electron scattering results from the same target with a number of significant differences observed and discussed. [ABSTRACT FROM AUTHOR]

We report integral, differential, and momentum-transfer cross sections for elastic scattering of electrons by tin tetrachloride ( SnCl 4). The scattering cross sections were calculated with the Schwinger multichannel method implemented with norm-conserving pseudopotentials, in the static-exchange and static-exchange plus polarization levels of approximation, for energies ranging from 0.01 eV to 30 eV. Our calculations show the presence of two resonant structures in the integral cross section located at 3.3 eV and 7.5 eV in the static-exchange approximation, while in the static exchange plus polarization approximation, these structures are centered around 1.2 eV and 5.6 eV. The symmetry decomposition of the integral cross section in both C 2 v and T d groups along with the analysis of the eigenvalues of the scattering Hamiltonian supports that the first resonance belongs to the T 2 symmetry and the second to the E symmetry. Our results also support that the ground state of the negative ion SnCl 4 − is stable, in agreement with the results of previous studies. The low-energy behavior of the s -wave cross section and the s -wave eigenphase support the presence of a Ramsauer–Townsend minimum at 0.1027 eV. The present integral, differential, and momentum-transfer cross sections in the static exchange approximation are in good agreement with the previous results reported by Joucoski and Bettega [J. Phys. B: At. Mol. Opt. Phys. 35, 4953 (2002)]. In the static exchange plus polarization approximation, our integral cross section shows a good qualitative agreement with the measured grand-total cross section of Możejko et al. [J. Chem. Phys. 151, 064305 (2019)]. [ABSTRACT FROM AUTHOR]

Measurements of the total electron scattering cross sections (TCSs) from benzene, in the impact energy range of 1–1000 eV, are presented here by combining two different experimental systems. The first utilizes a magnetically confined electron transmission beam for the lower energies (1–300 eV), while the second utilizes a linear transmission beam apparatus for the higher energies (100–1000 eV). These cross sections have also been calculated by means of two different theoretical methods, the Schwinger Multichannel with Pseudo Potential (SMCPP) procedure, employing two different approaches to account for the polarization of the target for impact energies between 0.1 and 15 eV, and the Independent Atom Model with the Screening Corrected Additivity Rule including Interference effect (IAM-SCAR+I) paradigm to cover the 10–10 000 eV impact energy range. The present results are compared with available theoretical and experimental data, with the level of accord being good in some cases and less satisfactory in others, and some predicted resonances have been identified. In particular, we found a π* shape resonance at 1.4 eV and another feature in the energy region 4.6–4.9 eV interpreted as a π* resonance (2B2g symmetry), which is a mixture of shape and a core excited resonance, as well as a Feshbach resonance at 5.87 eV associated with the 3s (a1g) Rydberg state. A Born-type formula to extrapolate TCS values for energies above 10 000 eV is also given. This study provides a complete set of TCS data, with uncertainty limits within 10%, ready to be used for modeling electron transport applications. [ABSTRACT FROM AUTHOR]

We report the results of ab initio calculations for elastic scattering and also for excitation of individual electronic states of para-benzoquinone (pBQ) by the impact of low-energy electrons. The calculations for elastic scattering were performed with the Schwinger multichannel method implemented with pseudopotentials (SMCPP) in the static-exchange (SE) plus polarization (SEP) approximation for energies up to 50 eV. The assignments for the resonance spectrum obtained in this study are, in general, in good agreement with previous results available in the literature. For electronic excitation by electron impact, the SMCPP method with N energetically open electronic states (Nopen), at either the static-exchange (Nopench-SE) or the static-exchange-plus-polarisation (Nopench-SEP) approximation, was employed to calculate the scattering amplitudes using a channel coupling scheme that ranges from the 1ch-SEP up to the 89ch-SE level of approximation, depending on the energy of interest. Integral cross sections (ICSs) and differential cross sections (DCSs) were obtained for incident electron energies lying between 15 eV and 50 eV. The study focuses on the influence of multichannel coupling effects for electronically inelastic processes, more specifically, on how the number of excited states included in the open-channel space impacts upon the convergence of the cross sections at intermediate and higher energies. In particular, we found that the magnitude of DCS and ICS results for electronic excitation decreases as more channels are included in the calculations. To the best of our knowledge, there are no other experimental or theoretical ICS or DCS results for excitation into individual electronic states of pBQ available in the literature between 15 and 50 eV against which we might compare the present calculations. [ABSTRACT FROM AUTHOR]

We report absolute experimental integral cross sections (ICSs) for the electron impact excitation of 6 bands (Bands 0-V) of unresolved electronic-states in para-benzoquinone, for incident electron energies between 20 and 40 eV. Absolute vibrational-excitation ICSs, for 3 composite vibrational bands (Bands I-III), are also reported in that same energy range. In addition, ICSs calculated within our independent atom model (IAM) with screening corrected additivity rule (SCAR) formalism, extended to account for interference (I) terms that arise due to the multi-centre nature of the scattering problem, are also reported. The sum of those ICSs gives the IAM-SCAR+I total cross section (TCS) for electron–para-benzoquinone scattering. Where possible, those calculated IAM-SCAR+I ICSs are compared against corresponding results from the present measurements with an acceptable level of accord being obtained. Similarly, we also present results from our Schwinger multichannel method with pseudopotential (SMCPP) calculations. Here elastic ICSs and ICSs corresponding to the Bands 0–III of unresolved electronic-states are presented, with agreement between the SMCPP electronic-state ICSs and those from our measurements being in good qualitative accord. The energy range of our SMCPP computations is 16–50 eV. Using the binary-encounter-Bethe (BEB) approach, total ionization cross sections for this collision system were computed. Those total ionization cross sections were then added to our SMCPP ICS results, to derive SMCPP/BEB TCSs that are typically in very good accord with those from our IAM-SCAR+I approach. [ABSTRACT FROM AUTHOR]

We report on theoretical elastic and experimental vibrational-excitation differential cross sections (DCSs) for electron scattering from para-benzoquinone (C6H4O2), in the intermediate energy range 15-50 eV. The calculations were conducted with two different theoretical methodologies, the Schwinger multichannel method with pseudopotentials (SMCPP) and the independent atom method with screening corrected additivity rule (IAM-SCAR) that also nowincorporates a further interference (I) term. The SMCPP with N energetically open electronic states (Nopen) at the static-exchange-pluspolarisation (Nopench-SEP) level was used to calculate the scattering amplitudes using a channel coupling scheme that ranges from 1ch-SE up to the 89ch-SEP level of approximation.We found that in going from the 38ch-SEP to the 89ch-SEP, at all energies considered here, the elastic DCSs did not change significantly in terms of both their shapes and magnitudes. This is a good indication that our SMCPP 89ch-SEP elastic DCSs are converged with respect to the multichannel coupling effect for the investigated intermediate energies. While agreement between our IAM-SCAR+I and SMCPP 89ch- SEP computations improves as the incident electron energy increases from 15 eV, overall the level of accord is only marginal. This is particularly true at middle scattering angles, suggesting that our SCAR and interference corrections are failing somewhat for this molecule below50 eV.We also report experimental DCS results, using a crossed-beam apparatus, for excitation of some of the unresolved ("hybrid") vibrational quanta (bands I-III) of para-benzoquinone. Those data were derived from electron energy loss spectra that were measured over a scattered electron angular range of 10°-90° and put on an absolute scale using our elastic SMCPP 89ch-SEP DCS results. The energy resolution of our measurements was ~80 meV, which is why, at least in part, the observed vibrational features were only partially resolved. To the best of our knowledge, there are no other experimental or theoretical vibrational excitation results against which we might compare the present measurements. [ABSTRACT FROM AUTHOR]

We report on a combination of experimental and theoretical investigations into the structure of electronically excited para-benzoquinone (pBQ). Here synchrotron photoabsorption measurements are reported over the 4.0-10.8 eV range. The higher resolution obtained reveals previously unresolved pBQ spectral features. Time-dependent density functional theory calculations are used to interpret the spectrum and resolve discrepancies relating to the interpretation of the Rydberg progressions. Electron-impact energy loss experiments are also reported. These are combined with elastic electron scattering cross section calculations performed within the framework of the independent atom model- screening corrected additivity rule plus interference (IAM-SCAR + I) method to derive differential cross sections for electronic excitation of key spectral bands.Ageneralized oscillator strength analysis is also performed, with the obtained results demonstrating that a cohesive and reliable quantum chemical structure and cross section framework has been established. Within this context, we also discuss some issues associated with the development of a minimal orbital basis for the single configuration interaction strategy to be used for our high-level low-energy electron scattering calculations that will be carried out as a subsequent step in this joint experimental and theoretical investigation. [ABSTRACT FROM AUTHOR]

In the present work we report elastic cross sections for electron scattering from acrylic acid (CH2 = CH-COOH) and its methylated derivatives, crotonic acid (CH3-CH = CH-COOH), methacrylic acid (H2C = C(CH3)COOH) and methyl acrylate (CH2 = CHCOOCH3). The calculations were performed with the Schwinger multichannel method for impact energies up to 15 eV. Two π * shape resonances were found in the component of the integral cross sections (ICSs) for the A ″ symmetry of all molecules. The resonance positions obtained for the acrylic acid are compared with existing experimental results for dissociative electron attachment. We investigated the influence of methylation through the comparison of the positions and widths of the shape resonances in the component of the ICS of the A ″, and the oscillation patterns in the differential cross sections of all molecules. We also present the momentum transfer cross section for electron scattering from all molecules studied. [ABSTRACT FROM AUTHOR]

We report differential and integral elastic cross sections for low-energy electron collisions with CF3Cl, CF2Cl2, and CFCl3 molecules for energies ranging from 0.1 eV to 30 eV. The calculations were performed using the Schwinger multichannel method with pseudopotentials in the static-exchange and static-exchange plus polarization approximations. The influence of the permanent electric dipole moment on the cross sections was included using the Born closure scheme. A very good agreement between our calculations and the experimental results of Jones [J. Chem. Phys. 84, 813 (1986)], Mann and Linder [J. Phys. B 25, 1621 (1992); 25, 1633 (1992)] and Hoshino et al. [J. Chem. Phys. 138, 214305 (2013)] was found. We also compare our results with the calculations of Beyer et al. [Chem. Phys. 255, 1 (2000)] using the R-matrix method, where we find good agreement with respect to the location of the resonances, and with the calculations of Hoshino et al. using the independent atom method with screening corrected additivity rule, where we find qualitative agreement at energies above 20 eV. Additional electronic structure calculations were carried out in order to help in the interpretation of the scattering results. The stabilization the lowest σ* resonance due to the exchange of fluorine by chlorine atoms (halogenation effect) follows a simple linear relation with the energy of the lowest unoccupied molecular orbitals and can be considered as a signature of the halogenation effect. [ABSTRACT FROM AUTHOR]

We report absolute experimental integral cross sections (ICSs) for electron impact excitation of bands of electronic-states in furfural, for incident electron energies in the range 20-250 eV. Wherever possible, those results are compared to corresponding excitation cross sections in the structurally similar species furan, as previously reported by da Costa et al. [Phys. Rev. A 85, 062706 (2012)] and Regeta and Allan [Phys. Rev. A 91, 012707 (2015)]. Generally, very good agreement is found. In addition, ICSs calculated with our independent atom model (IAM) with screening corrected additivity rule (SCAR) formalism, extended to account for interference (I) terms that arise due to the multi-centre nature of the scattering problem, are also reported. The sum of those ICSs gives the IAM-SCAR+I total cross section for electron-furfural scattering. Where possible, those calculated IAM-SCAR+I ICS results are compared against corresponding results from the present measurements with an acceptable level of accord being obtained. Similarly, but only for the band I and band II excited electronic states, we also present results from our Schwinger multichannel method with pseudopotentials calculations. Those results are found to be in good qualitative accord with the present experimental ICSs. Finally, with a view to assembling a complete cross section data base for furfural, some binary-encounter-Bethe-level total ionization cross sections for this collision system are presented. [ABSTRACT FROM AUTHOR]

We report results from a joint experimental and theoretical investigation into electron scattering from the important industrial species furfural (C5H4O2). Specifically, differential cross sections (DCSs) have been measured and calculated for the electron-impact excitation of the electronic states of C5H4O2. The measurements were carried out at energies in the range 20-40 eV, and for scattered-electron angles between 10° and 90°. The energy resolution of those experiments was typically ~80 meV. Corresponding Schwinger multichannel method with pseudo-potential calculations, for energies between 6-50 eV and with and without Born-closure, were also performed for a sub-set of the excited electronic-states that were accessed in the measurements. Those calculations were undertaken at the static exchange plus polarisation-level using a minimum orbital basis for single configuration interaction (MOB-SCI) approach. Agreement between the measured and calculated DCSs was qualitatively quite good, although to obtain quantitative accord, the theory would need to incorporate even more channels into the MOB-SCI. The role of multichannel coupling on the computed electronic-state DCSs is also explored in some detail. [ABSTRACT FROM AUTHOR]

We report cross sections for electron-impact excitation of vibrational quanta in furfural, at intermediate incident electron energies (20, 30, and 40 eV). The present differential cross sections are measured over the scattered electron angular range 10-90, with corresponding integral cross sections subsequently being determined. Furfural is a viable plant-derived alternative to petrochemicals, being produced via low-temperature plasma treatment of biomass. Current yields, however, need to be significantly improved, possibly through modelling, with the present cross sections being an important component of such simulations. To the best of our knowledge, there are no other cross sections for vibrational excitation of furfural available in the literature, so the present data are valuable for this important molecule. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We report differential cross section results from an experimental investigation into the electron impact excitation of a number of the low-lying composite (unresolved) vibrational modes in phenol (C6H5OH). The measurements were carried out at incident electron energies in the range 15-40 eV and for scattered-electron angles in the range 10-90°. The energy resolution of those measurements was typically ~80 meV. Calculations, using the GAMESS code, were also undertaken with a B3LYP/aug-cc-pVDZ level model chemistry, in order to enable us to assign vibrational modes to the features observed in our energy loss spectra. To the best of our knowledge, the present cross sections are the first to be reported for vibrational excitation of the C6H5OH molecule by electron impact. [ABSTRACT FROM AUTHOR]

We report results from a joint theoretical and experimental investigation into electron scattering from the important organic species phenol (C6H5OH). Specifically, differential cross sections (DCSs) have been measured and calculated for the electron-impact excitation of the electronic states of C6H5OH. The measurements were carried out at energies in the range 15-40 eV, and for scattered-electron angles between 10° and 90°. The energy resolution of those experiments was typically ~80 meV. Corresponding Schwinger multichannel method with pseudo-potentials calculations, with and without Born-closure, were also performed for a sub-set of the excited electronic-states that were accessed in the measurements. Those calculations were conducted at the static exchange plus polarisation (SEP)-level using a minimum orbital basis for single configuration interaction (MOBSCI) approach. Agreement between the measured and calculated DCSs was typically fair, although to obtain quantitative accord, the theory would need to incorporate even more channels into the MOBSCI. [ABSTRACT FROM AUTHOR]

We present experimental electron-energy loss spectra (EELS) that were measured at impact energies of 20 and 30 eV and at angles of 90° and 10°, respectively, with energy resolution ~70 meV. EELS for 250 eV incident electron energy over a range of angles between 3° and 50° have also been measured at a moderate energy resolution (~0.9 eV). The latter spectra were used to derive differential cross sections and generalised oscillator strengths (GOS) for the dipole-allowed electronic transitions, through normalization to data for elastic electron scattering from benzene. Theoretical calculations were performed using time-dependent density functional theory and single-excitation configuration interaction methods. These calculations were used to assign the experimentally measured spectra. Calculated optical oscillator strengths were also compared to those derived from the GOS data. This provides the first investigation of all singlet and triplet excited electronic states of phenol up to the first ionization potential. [ABSTRACT FROM AUTHOR]

We report on the shape resonance spectra of uracil, 5-fluorouracil, and 5-chlorouracil, as obtained from fixed-nuclei elastic scattering calculations performed with the Schwinger multichannel method with pseudopotentials. Our results are in good agreement with the available electron transmission spectroscopy data, and support the existence of three p* resonances in uracil and 5-fluorouracil. As expected, the anion states are more stable in the substituted molecules than in uracil. Since the stabilization is stronger in 5-chlorouracil, the lowest p* resonance in this system becomes a bound anion state. The present results also support the existence of a low-lying s*CCl shape resonance in 5-chlorouracil. Exploratory calculations performed at selected C-Cl bond lengths suggest that the s*CCl resonance could couple to the two lowest p* states, giving rise to a very rich dissociation dynamics. These facts would be compatible with the complex branching of the dissociative electron attachment cross sections, even though we cannot discuss any details of the vibration dynamics based only on the present fixed-nuclei results. [ABSTRACT FROM AUTHOR]

We report elastic integral and differential cross sections for electron scattering from the aza-derivatives of pyrrole, furan, and thiophene, namely, pyrazole, imidazole, isoxazole, oxazole, isothiazole, and thiazole. The calculations were performed within the Schwinger multichannel method with pseudopotentials, with inclusion of static, exchange, and polarization interactions, for energies up to 10 eV. We found two π* shape resonances and a high-lying σ* shape resonance in each system. A sharp low-energy σ* resonance was also identified in isothiazole and thiazole. Pyrazole and imidazole presented yet a broad low-lying σ* resonance. The positions of the resonances agree very well with existing experimental results. We discuss the similarities and differences among the resonances of these compounds. [ABSTRACT FROM AUTHOR]

We report on elastic integral, momentum transfer, and differential cross sections for collisions of low-energy electrons with thiophene molecules. The scattering calculations presented here used the Schwinger multichannel method and were carried out in the static-exchange and static-exchange plus polarization approximations for energies ranging from 0.5 eV to 6 eV. We found shape resonances related to the formation of two long-lived π* anion states. These resonant structures are centered at the energies of 1.00 eV (2.85 eV) and 2.82 eV (5.00 eV) in the static-exchange plus polarization (static-exchange) approximation and belong to the B1 and A2 symmetries of the C2v point group, respectively. Our results also suggest the existence of a σ* shape resonance in the B2 symmetry with a strong d-wave character, located at around 2.78 eV (5.50 eV) as obtained in the static-exchange plus polarization (static-exchange) calculation. It is worth to mention that the results obtained at the static-exchange plus polarization level of approximation for the two π* resonances are in good agreement with the electron transmission spectroscopy results of 1.15 eV and 2.63 eV measured by Modelli and Burrow [J. Phys. Chem. A 108, 5721 (2004)]. The existence of the σ* shape resonance is in agreement with the observations of Dezarnaud-Dandiney et al. [J. Phys. B 31, L497 (1998)] based on the electron transmission spectra of dimethyl(poly)sulphides. A comparison among the resonances of thiophene with those of pyrrole and furan is also performed and, altogether, the resonance spectra obtained for these molecules point out that electron attachment to π* molecular orbitals is a general feature displayed by these five-membered heterocyclic compounds. [ABSTRACT FROM AUTHOR]

We present novel experimental results of negative ion formation of halothane (C2HBrClF3) upon electron transfer from hyperthermal neutral potassium atoms (K°) in the collision energy range of 8–1000 eV. The experiments were performed in a crossed molecular beam setup allowing a comprehensive analysis of the time-of-flight (TOF) mass negative ions fragmentation pattern and a detailed knowledge of the collision dynamics in the energy range investigated. Such TOF mass spectra data show that the only negative ions formed are Br−, Cl− and F−, with a strong energy dependence in the low-energy collision region, with the bromine anion being the most abundant and sole fragment at the lowest collision energy probed. In addition, potassium cation (K+) energy loss spectra in the forward scattering direction were obtained in a hemispherical energy analyser at different K° impact energies. In order to support our experimental findings, ab initio quantum chemical calculations have been performed to help interpret the role of the electronic structure of halothane. Potential energy curves were obtained along the C–X (X = Br, Cl) coordinate to lend support to the dissociation processes yielding anion formation. [ABSTRACT FROM AUTHOR]

In this paper we report original measurements of total cross sections (TCSs) for positron scattering from the cyclic ethers oxirane (C2H4O), 1,4-dioxane (C4H8O2), and tetrahydropyran (C5H10O). The present experiments focus on the low energy range from ∼0.2 to 50 eV, with an energy resolution smaller than 300 meV. This study concludes our systematic investigation into TCSs for a class of organic compounds that can be thought of as sub-units or moieties to the nucleotides in living matter, and which as a consequence have become topical for scientists seeking to simulate particle tracks in matter. Note that as TCSs specify the mean free path between collisions in such simulations, they have enjoyed something of a recent renaissance in interest because of that application. For oxirane, we also report original Schwinger multichannel elastic integral cross section (ICS) calculations at the static and static plus polarisation levels, and with and without Born-closure that attempts to account for the permanent dipole moment of C2H4O. Those elastic ICSs are computed for the energy range 0.5-10 eV. To the best of our knowledge, there are no other experimental results or theoretical calculations against which we can compare the present positron TCSs. However, electron TCSs for oxirane (also known as ethylene oxide) and tetrahydropyran do currently exist in the literature and a comparison to them for each species will be presented. [ABSTRACT FROM AUTHOR]

The authors report integral, differential and momentum transfer cross sections for elastic scattering of low-energy electrons by C4H4O (furan) molecules. Their calculations employed the Schwinger multichannel method with pseudopotentials and were performed in the static-exchange and in the static-exchange plus polarization approximations. The authors found two shape resonances located around 2.1 and 4.2 eV that belong to the B1 and A2 symmetries of the C2v group, respectively. The authors’ results are consistent with recent measurements of vertical electron attachment energies. [ABSTRACT FROM AUTHOR]

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° and 120° 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 π* 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. [ABSTRACT FROM AUTHOR]

In the present work we report cross sections for electron collisions with the isomers propene (C3H6) and cyclopropane (c-C3H6). Electron-scattering differential cross sections (DCS) are reported for measurements carried out for energies 1.5–100 eV and the angular range of 20°–120°. Elastic integral cross sections (ECS), DCS, and momentum-transfer cross sections (MTCS) are reported for calculations carried out using the Schwinger multichannel method with pseudopotentials for the energy range of 2.0–40 eV and angular range of 0°–180°. The resemblance of the π* shape resonance in the cross sections, observed at 1.5–2.0 eV for propene, to those in C2H4 and C2F4 clearly points to the effect of the double bond in the molecular structures for these molecules. Below 60 eV, we observed clear differences in peak positions and magnitudes between the DCS, ECS, and MTCS for C3H6 and c-C3H6, which we view as the isomer effect. [ABSTRACT FROM AUTHOR]

We report calculated elastic and inelastic cross sections for low-energy electron collisions with methylsilane, CH[SUB3]SiH[SUB3], obtained using the Schwinger multichannel method. The elastic cross sections, obtained within the static-exchange approximation, are compared with elastic results for C[SUB2]H[SUB6] and Si[SUB2]H[SUB6]. Electron-impact excitation cross sections were computed for sixteen electronic states arising from excitation out of the two highest-lying valence orbitals. The dissociation of the lowest few states was examined through limited electronic-structure calculations, which indicated that the 2[SUP1,3] A[SUB1] states dissociate to CH[SUB3]SiH + [SUB2] while the 1[SUP1,3]E states dissociate to CH[SUB3] + SiH[SUB3]. [ABSTRACT FROM AUTHOR]

We calculated integral and differential cross sections for scattering of low-energy electrons by two groups of hydrides from 10 to 30 eV. The first group is composed by the hydrides of elements in the same column of the Periodic Table and includes PH3, AsH3, and SbH3. The second group is formed by hydrides in the same row and includes SnH4, SbH3, TeH2, and HI. The calculations employed the Schwinger multichannel method with norm-conserving pseudopotentials [M.H.F. Bettega, L.G. Ferreira, and M.A.P. Lima, Phys. Rev. A 47, 1111 (1993)]. Our goal is to find similarities and differences in the cross sections in these two groups. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report elastic integral, differential, and momentum transfer cross sections from 10 to 30 eV for electron scattering by SnH4 and PbH4, obtained using the Schwinger Multichannel Method with Pseudopotentials [M. H. F. Bettega, L. G. Ferreira, and M. A. P. Lima, Phys. Rev. A 47, 1111 (1993)]. With these molecules we close the series of XH4 molecules, with X=C, Si, Ge, Sn, Pb. We compare the present results with those obtained previously for CH4, SiH4, and GeH4. We find similarities in the cross sections for SiH4, GeH4, SnH4, and PbH4 and a distinctive behavior of CH4. We discuss the role of the center atom size in the scattering process. To our knowledge this is the first ab initio calculation of the SnH4 and PbH4 electron scattering cross sections. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Total electron scattering cross sections, from para-benzoquinone, for impact energies ranging between 1 to 200 eV, have been obtained by measuring the attenuation of a linear electron beam under magnetic confinement conditions. Random uncertainty limits on these values have been found to be within 5%. Systematic errors, due to the axial magnetic beam conditions in combination with the acceptance angle of the detector, have been evaluated by integrating our calculated independent atom model with the screening corrected additivity rule and interference term elastic differential cross sections over that detection acceptance angle. Our previous calculations and measurements on this molecule (Jones et al., J. Chem. Phys., 2018, 148, 124312 and J. Chem. Phys., 2018, 148, 204305), have been compiled and complemented with new elastic and inelastic scattering cross section calculations in order to obtain a comprehensive cross section data base, within the considered energy range, for modelling purposes. The self-consistency of the present data set has been evaluated by simulating the electron transport of 15 eV electrons in para-benzoquinone, and comparing those results with the observed transmitted intensity distribution. [ABSTRACT FROM AUTHOR]

Angle resolved electron energy loss spectra (EELS) for para-benzoquinone (C6H4O2) have been recorded for incident electron energies of 20, 30, and 40 eV. Measured differential cross sections (DCSs) for electronic band features, composed of a combination of energetically unresolved electronic states, are subsequently derived from those EELS. Where possible, the obtained DCSs are compared with those calculated using the Schwinger multichannel method with pseudopotentials. These calculations were performed using a minimum orbital basis single configuration interaction framework at the static exchange plus polarisation level. Here, quite reasonable agreement between the experimental cross sections and the theoretical cross sections for the summation of unresolved states was observed. [ABSTRACT FROM AUTHOR]

We present a comparative study on the calculated cross sections obtained for the elastic collisions of low-energy electrons with the amino acid proline (C5H9NO2) and its building block pyrrolidine (C4H9N). We employed the Schwinger multichannel method implemented with pseudopotentials to compute integral, differential, and momentum transfer cross sections in the static-exchange plus polarization approximation, for energies up to 15 eV. We report three shape resonances for proline at around 1.7 eV, 6.8 eV, and 10 eV and two shape resonances for pyrrolidine centered at 7 eV and 10.2 eV. The present resonance energies are compared with available experimental data on vertical attachment energies and dissociative electron attachment, where a good agreement is found. From the comparison of the present results with available calculated cross sections for the simplest carboxylic acid, formic acid (HCOOH), and from electronic structure calculations, we found that the first resonance of proline, at 1.7 eV, is due the presence of the carboxylic group, whereas the other two structures, at 6.8 eV and 10 eV, clearly arise from the pyrrolidine ring. A comparison between the differential cross sections for proline and pyrrolidine at some selected energies of the incident electron is also reported in this paper. [ABSTRACT FROM AUTHOR]

We report momentum transfer cross sections for elastic collisions of low-energy electrons with the HCOOH...(H2O)n complexes, with n = 1, 2, in liquid phase. The scattering cross sections were computed using the Schwinger multichannel method with pseudopotentials in the static-exchange and static-exchange plus polarization approximations, for energies ranging from 0.5 eV to 6 eV. We considered ten different structures of HCOOH...H2O and six structures of HCOOH...(H2O)2 which were generated using classical Monte Carlo simulations of formic acid in aqueous solution at normal conditions of temperature and pressure. The aim of this work is to investigate the influence of microsolvation on the π* shape resonance of formic acid. Previous theoretical and experimental studies reported a π* shape resonance for HCOOH at around 1.9 eV. This resonance can be either more stable or less stable in comparison to the isolated molecule depending on the complex structure and the water role played in the hydrogen bond interaction. This behavior is explained in terms of (i) the polarization of the formic acid molecule due to the water molecules and (ii) the net charge of the solute. The proton donor or acceptor character of the water molecules in the hydrogen bond is important for understanding the stabilization versus destabilization of the π* resonances in the complexes. Our results indicate that the surrounding water molecules may affect the lifetime of the π* resonance and hence the processes driven by this anion state, such as the dissociative electron attachment. [ABSTRACT FROM AUTHOR]

We report elastic and electronically inelastic cross sections for low-energy electron scattering by pentafluoroethane, C[sub 2]HF[sub 5]. Our calculations were performed using the Schwinger multichannel method. For elastic scattering, we calculated integral, differential, and momentum transfer cross sections for energies from 5 to 50 eV. In the inelastic case, we obtained integral and differential cross sections for electron-impact excitation of the 1 [sup 1,3]A[sup ′] and 2 [sup 1,3]A[sup ′] excited states at the three-channel level of approximation. At higher energies, the elastic differential cross sections are quite similar to existing theoretical results for C[sub 2]F[sub 6]. Limited electronic-structure calculations were carried out to explore the dissociation behavior of the excited states. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We present elastic cross sections obtained from ab initio calculations for low-energy electron scattering by benzene, C[sub 6]H[sub 6]. The calculations employed the Schwinger multichannel method as implemented for parallel computers within both the static-exchange and static-exchange-polarization approximations. We compare our results with other theoretical calculations and with available experimental data. In general, agreement is good. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]