Cross section and asymmetry parameter calculations for the C 1s photoionization of CH4, CF4, and CCl4

We have computed cross sections and asymmetry parameters for the C 1s photoionization of CX4 (X=H, F, Cl) using the Schwinger variational method with Pade corrections. We present a comparative study that shows the influence of the identity of the X atom on the computed cross sections. Predicted cross sections are in good agreement with available photoionization and photoabsorption experimental data. We conclude that the presence of heavy outer atoms produces resonance structures in the photoionization cross sections and in the asymmetry parameters. We find a single nonvalence resonant state in the photoionization of CF4 and multiple resonances in CCl4 that have significant d-orbital character in the vicinity of the Cl atoms.68

25-state calculation for e(-)-Na-2 scattering

We use the Schwinger multichannel method with pseudopotentials to study low energy e(-)-Na-2 scattering. Our cross sections, for impact energies from 0 to 10 eV, include polarization effects and up to 25 open channels related to all electronic states lying below 3.5 eV. Our results predict prominent threshold effects due to a very intense coupling between the B(1)Pi(u) state and the elastic channel in an energy region where there is no experimental data. Our total 25-state cross sections are in very good agreement with available experimental data for energies below about 4 eV. [S0031-9007(98)07561-9].81183832383

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

Elastic scattering of low-energy electrons by CF3Cl, CF3Br and CF3I

We report integral, differential and momentum transfer cross sections for elastic scattering of low-energy electrons by CF3X (X = Cl, Br, 1) molecules. We use the Schwinger multichannel method with pseudopotentials (Bettega et al 1993 Phys. Rev. A 47 1111) at the static exchange approximation. Our calculations cover the energy range between 5 and 30 eV We compare our results with available theoretical and experimental results for CF3Cl and CF3I, and in general find good agreement. In particular, our results show the shape resonances belonging to the A(1) and E representations of the C-3v group that have been reported by previous work.3661263127

Calculation of elastic scattering cross sections of low-energy electrons by PbH4 and SnH4

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 XH(4) 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. (C) 1995 American Institute of Physics.10324105661057

Electronic excitation of H-2 by electron impact using soft norm-conserving pseudopotentials

We calculate electronic excitation cross sections for the b (3) Sigma(u)(+) a (3) Sigma(g)(+) c (3) Pi(g), and d (3) Pi(u), states of H-2 by electron impact. Our results were obtained with the Schwinger multichannel method with pseudopotentials and real potentials at the two-channel level of approximation. Pseudo-H atoms are used to generate H-2 molecules with almost the same low-energy spectrum as the real molecules. We show that the dynamics of the electronic excitation process of the pseudomolecules by electron impact is very similar to the real case. Our results support the idea that pseudopotentials can be used to obtain reliable molecular electronic excitation cross sections by low-energy electron impact, confirming the expectations of previous studies with CH2O [Bettega et al., Phys. Rev. A 25, 1111 (1993)] and HBr [Rescigno, J. Chem. Phys. 104, 125 (1996)].5465435543

Elastic and rotationally inelastic cross sections for low-energy electron scattering by SO2 molecules

We show rotationally summed and rotationally inelastic differential, integral and momentum transfer cross sections for electron scattering by SO2 in the 3-30 eV impact energy range in the static exchange approximation. Our results were obtained with the Schwinger multichannel method with pseudopotentials, including a first Born approximation Ib describe the influence of the molecular permanent dipole moment on the scattering cross sections. The rotational excitation cross sections were obtained through the adiabatic-nuclei-rotation approximation. Our results show good agreement with available experimental and theoretical data. The rotationally inelastic cross sections were found to be very large.32235523553

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. All tables are available in the electronic version of the paper only [on the world wide web at http://www.sbf.if.usp.br/bjp/Vol31/Num1/].311212

Applications of the Schwinger multichannel method with pseudopotentials to electron scattering from polyatomic molecules I. Elastic cross sections

This paper is a data basis which includes tables of integral, differential, and momentum transfer cross sections for elastic electron scattering from CF4, CCl4, SiCl4, SiBr4, SiI4, CH3F CH2F2, CHF3, CH3Cl, CH2Cl2, CHCl3, CF3Cl, CF2Cl2, CFCl3, CH3Br, CH3I, SiH3Cl, SiH3Br, SiH3I, GeH3Cl, GeH3Br, SnH3Br, C2H6, Si2H6. Ge2H6, B2H6, Ga2H6, H2O, H2S, H2Se, H2Te, trimethylarsine (TMAs), N2O, and O-3. These tables show our new results, along with some of our previously published cross sections, and can easily be compared to future experimental data and other new theoretical results. Our scattering amplitudes were calculated using the Schwinger multichannel method with norm-conserving pseudopotentials. Our results are in good agreement with other theoretical data and experimental results when available. All tables are available in the electronic version of the paper only [on the world wide web at http://www.sbf.if.usp.br/bjp/Vol31/Num1/.].311152