Electronic excitation of XH4 (X = C,Si,Ge,Sn,Pb) by electron impact

We calculate integral cross sections for the electronic excitation to the T-3(2) states of XH4 (X= C,Si,Ge,Sn,Pb) by electron impact. This is the lowest-lying excited state of these molecules. Our results were obtained with the Schwinger multichannel method with pseudopotentials at the two-state level of approximation. In the case of CH4 we compare our results with previous results of an all-electron calculation obtained at the same level of approximation, in which case we found an excellent agreement between the two calculations. Though these molecules are very similar, after discarding the cores, as the pseudopotential technique does, the inelastic cross sections are very distinctive and do not have a monotonic behavior with increasing proton number Z of the central atom.5764987499

Cross sections for collisions of low-energy electrons with the hydrides PH3, AsH3, SbH3, SnH4, TeH2, and HI

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. (C) 1996 American Institute of Physics.10531029103

Polarization effects on electronic excitation of molecules by low-energy electron impact: Study on e(-)-furan scattering

The Schwinger multichannel method is applied to study the influence of polarization effects on the electronic excitation of the furan molecule by low-energy electron impact. We discuss the importance of inclusion of these effects through the comparison of theoretical results for the electronic excitation of the (3)B(2) state of furan obtained with and without the proper treatment of the polarization of the target. The electron-furan scattering presents two prominent shape resonances in the (2)A(2) and (2)B(1) symmetries at around the electronic excitation threshold of the (3)B(2) state (3.7 eV). At this low-energy, the inclusion of polarization effects in the calculation moves to lower energies the resonances positions obtained either in the close-coupling or in the static-exchange level of approximation. This phenomenon strongly influences the electronic excitation process. The present results show that a simple close-coupling calculation cannot be applied for molecular systems with low-energy electronic excitation thresholds around misplaced resonances.77

Low-energy electron collisions with C4H6 isomers

We report integral, differential, and momentum-transfer cross sections for elastic scattering of low-energy electrons by C4H6 isomers, namely, 1,3-butadiene, 2-butyne, and cyclobutene. We use the Schwinger multichannel method with pseudopotentials [M. H. F. Bettega, L. G. Ferreira, and M. A. P. Lima, Phys. Rev. A-47, 1111 (1993)] at the static-exchange approximation to compute the cross sections for energies from 10 to 60 eV. In particular, we discuss the isomer effect, reported by experimental studies for isomers Of C3H4 and C4H6. We also calculate the total ionization cross section using the binary-encounter-Bethe model for 2-butyne and 1,3-butadiene, and estimate the inelastic cross section for these two isomers.69

Low-energy electron scattering by CF4, CCl4, SiCl4, SiBr4, and SiI4

in this paper, we show elastic and rotationally inelastic cross-section calculations of low-energy electron scattering by CF4, CCl4, SiCl4, SiBr4, and SiI4. The fixed-nuclei static-exchange scattering amplitudes were obtained with the Schwinger multichannel method with soft norm-conserving pseudopotentials. We show elastic integral and differential cross sections and discuss the role of the basis set on the nature of some structures seen in a previous publication [A. P. P; Natalense et al., Phys. Rev. A 52, R1 (1995)]. We have attributed these structures to linear dependency in the basis set caused by the symmetric combination (x(2)+y(2)+z(2))exp(-ar(2)). The rotational cross sections were calculated with the help of the adiabatic-nuclei-rotation approximation. Our results are in good agreement with available experimental data. The sums of 0 -->0,3,4,6 rotational cross sections in general show good agreement with the elastic (rotationally unresolved) ones. The rotationally summed integral cross section agrees within 0.3% with the elastic integral cross section for CF4 at 7.5 eV, and within 26% for SiI4 at 30 eV. It was found that rotationally inelastic cross sections are considerably large for such molecules, because the heavy peripheral atoms play a significant role as scattering centers. [S1050-2947(99)00611-3].6053684369

A comparative study of elastic scattering of low-energy electrons by boron, aluminum and gallium trihalides

In this paper we present integral, differential and momentum transfer cross sections for elastic scattering of low-energy electrons by some metal-halogen molecular compounds, namely, BF3, BCl3, BBr3, BI3, AlF3, AlCl3, AlBr3, AlI3, GaF3, GaCl3, GaBr3, and GaI3. The pseudopotential based calculations were carried out with the Schwinger multichannel method at the static-exchange level of approximation. It is the purpose of this work to make a comparative study of the scattering processes involving aluminum and gallium trihalides with previous results for the boron ones [M. H. F. Bettega, Phys. Rev. A 61, 042703 (2000)]. We find through direct comparison of the elastic cross sections that, at low energies, the scattering processes are mainly dominated by the halogen atoms. (C) 2003 American Institute of Physics.1181758

Low-energy electron collisions with acetic acid

We present cross sections for elastic collisions of low-energy electrons with acetic acid. We employed the Schwinger multichannel method with pseudopotentials in the static-exchange and static-exchange plus polarization approximations, for energies ranging from 0.1 to 10 eV. We found a pi(*) shape resonance around 1.7 eV, corresponding to the A(') symmetry of the C(s) group. This resonant state was assigned to the experimental dissociative electron attachment peak at 1.7 eV yielding CH(3)COO(-)+H. We also performed a series of electronic structure calculations using a small basis set for acetic, formic, and trifluoroacetic acids, which exhibit a similar behavior with respect to the dissociative electron attachment. We believe that hydrogen elimination triggered off by electron capture into a pi(*) resonance could be a general property of carboxylic acids.79

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 (nu(2) and nu(9)) stretching and the combined C-F (nu(3)) stretching and CH2 (nu(11)) 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 B-2, B-1, and A(1) 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. (c) 2007 American Institute of Physics.1261

The Schwinger Variational Method

Variational methods have proven invaluable in theoretical physics and chemistry, both for bound state problems and for the study of collision phenomena. For collisional problems they can be grouped into two types: those based on the Schroedinger equation and those based on the Lippmann-Schwinger equation. The application of the Schwinger variational (SV) method to e-molecule collisions and photoionization has been reviewed previously. The present chapter discusses the implementation of the SV method as applied to e-molecule collisions

Electron collisions with furan

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 B-1 and A(2) symmetries of the C-2v group, respectively. The authors' results are consistent with recent measurements of vertical electron attachment energies. (C) 2007 American Institute of Physics.1261