M. H. F. Bettega

Universidade Federal do Paraná

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Marco A. P. Lima

Universidade Estadual de Campinas (UNICAMP)

103

Márcio T. do N. Varella

Universidade de São Paulo

Romarly F. da Costa

Universidade Federal do ABC

Alessandra Souza Barbosa

Universidade Federal do Paraná

Sergio d’A. Sanchez

Universidade Federal do Paraná

M. J. Brunger

Flinders University

Giseli M. Moreira

Universidade Estadual do Centro-Oeste

G. Garcı́a

Consejo Superior de Investigaciones Científicas

P. Limão-Vieira

Universidade Nova de Lisboa

M. A. Khakoo

California State University, Fullerton

Cooperative Institutions

Flinders University

California State University, Fullerton

Universidade Federal do Paraná

Universidade Nova de Lisboa

Universidade Estadual de Campinas (UNICAMP)

James Cook University

University of Malaya

Consejo Superior de Investigaciones Científicas

Instituto de Física Fundamental

Australian National University

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

Journal of Quantitative Spectroscopy and Radiative Transfer (2023)

Pedro A. S. Randi Sarvesh Kumar Ana Lozano M. H. F. Bettega Søren Vrønning Hoffmann

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.

Rydberg constant

Coupled cluster

Rydberg state

10.1016/j.jqsrt.2023.108597

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Citations (3)

Low-energy electron scattering by H2O, H2S, H2Se, and H2Te

The Journal of Chemical Physics (1999)

Márcio T. do N. Varella M. H. F. Bettega Marco A. P. Lima Luiz G. Ferreira

We report elastic differential, integral, and momentum transfer cross-sections for H2X molecules (X: O, S, Se, and Te) obtained at the static exchange level of approximation. The energy range considered was from 2 up to 30 eV for H2O and from 5 up to 30 eV for the other molecules. Our calculations were performed with the Schwinger multichannel method with pseudopotentials [M. H. F. Bettega, L. G. Ferreira, and M. A. P. Lima, Phys. Rev. A 47, 1111 (1993)], combined with a Born closure procedure in order to account for the long-range potential due to the permanent dipole moment of the targets. Our calculated cross-sections for H2O and H2S are in good agreement with other theoretical results. Agreement with available experimental data is also encouraging. It was found that molecular size plays a crucial role in the scattering process. The influence of heavy and H atoms in the collisions is also discussed. For the integral cross-sections of the heavier molecules we also investigated incident energies below 5 eV, looking for possible shape resonances. Through the symmetry decomposition of the integral cross-sections and the eigenphase sum analysis, we found shape resonances for H2S, H2Se, and H2Te at the B2 symmetry. For H2Te, we have also found a shape resonance at the A2 symmetry. For all molecules a very broad structure was found at the A1 symmetry. This is the first work to report such resonances for H2Se and H2Te.

Shape resonance

Momentum transfer

10.1063/1.480017

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Citations (66)

Elastic Positron Collisions with 1,1-Difluoroethylene

The Journal of Physical Chemistry A (2021)

Rafael O. Lima Giseli M. Moreira Alessandra Souza Barbosa M. H. F. Bettega Sergio d’A. Sanchez

This work reports a theoretical investigation on the elastic-positron collision with the 1,1-difluoroethylene molecule for energies up to 10 eV. We have employed the Schwinger multichannel method in the static-plus polarization level of approximation to obtain the integral and differential cross sections. In order to account for the long-range potential due to the permanent dipole moment of the target, the Born-closure procedure has been employed. Also, our present differential cross sections have been applied to estimate a correction to the total cross section measurements available in the literature.

Scattering cross-section

10.1021/acs.jpca.1c04047

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Citations (2)

Elastic scattering of low-energy electrons byXH3YH3 Physical Review A (2003)

C. Maia M. H. F. Bettega

In this paper, we present cross sections for elastic scattering of low-energy electrons by $X{\mathrm{H}}_{3}Y{\mathrm{H}}_{3}$ $(X,$ $Y=\mathrm{C},$ Si, Ge, and Sn) molecules. To compute the cross sections we used the Schwinger multichannel method with pseudopotentials at the fixed-nuclei static-exchange approximation. In order to make a comparative study of the scattering cross sections of the $X{\mathrm{H}}_{3}Y{\mathrm{H}}_{3}$ molecules, which have the same number of valence electrons, we also present the results of previous calculations for ${\mathrm{C}}_{2}{\mathrm{H}}_{6},$ ${\mathrm{Si}}_{2}{\mathrm{H}}_{6},$ and ${\mathrm{Ge}}_{2}{\mathrm{H}}_{6}.$

Valence electron

10.1103/physreva.67.042710

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Citations (2)

Low-energy electron scattering by N, P, As and Sb

Journal of Physics B Atomic Molecular and Optical Physics (1998)

M. H. F. Bettega Marco A. P. Lima Leonardo L. G. Ferreira

We report elastic integral, momentum transfer and differential cross sections from 10-30 eV for electron scattering by (X = N, P, As, Sb). These results were obtained at the static-exchange approximation with the Schwinger Multichannel Method with Pseudopotentials [M H F Bettega, L G Ferreira and M A P Lima 1993 Phys. Rev. A 47 1111]. Our results for are in good agreement with experimental data. We also compare our results with previous calculations on (X = P, As, Sb) [M H F Bettega, M A P Lima and L G Ferreira 1996 J. Chem. Phys. 105 1029] and found, as expected, that the cross sections are larger than the corresponding cross sections.

Momentum transfer

Electron scattering

Momentum (technical analysis)

10.1088/0953-4075/31/9/021

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Citations (8)

A comparison of experimental and theoretical low energy positron scattering from furan

The Journal of Chemical Physics (2020)

Z. Cheong Giseli M. Moreira M. H. F. Bettega F. Blanco G. Garcı́a

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.

Positronium

Mott scattering

Quasielastic scattering

10.1063/5.0027874

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Citations (3)

Electron collisions with furan

The Journal of Chemical Physics (2007)

M. H. F. Bettega Marco A. P. Lima

The authors report integral, differential and momentum transfer cross sections for elastic scattering of low-energy electrons by C(4)H(4)O (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.

Momentum transfer

Electron scattering

Electron exchange

10.1063/1.2739514

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Citations (23)

Electron collisions with CS₂

Journal of Physics B Atomic Molecular and Optical Physics (2005)

M. H. F. Bettega Marco A. P. Lima L. G. Ferreira

We present elastic integral and differential cross sections for electron collisions with CS2 molecules for energies up to 10 eV. To compute the cross sections we employed the Schwinger multichannel method implemented with pseudopotentials at the static-exchange plus polarization approximation. In particular, our integral cross section shows a sharp increase near zero energy, which is an indication of the existence of an s-wave virtual state, followed by a Ramsauer–Townsend minimum around 0.7 eV. Our results agree well with available experimental and theoretical results.

10.1088/0953-4075/38/13/003

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Citations (8)

Electron Collisions with Hexafluorobenzene, C_6F_6

APS Annual Gaseous Electronics Meeting Abstracts (1999)

Carl Winstead Vincent McKoy M. H. F. Bettega

Hexafluorobenzene

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Shape resonance spectra of uracil, 5-fluorouracil, and 5-chlorouracil

The Journal of Chemical Physics (2014)

Fábris Kossoski M. H. F. Bettega Márcio T. do N. Varella

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 π* 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 π* resonance in this system becomes a bound anion state. The present results also support the existence of a low-lying \documentclass[12pt]{minimal}\begin{document}$\sigma _{\rm CCl}^*$\end{document}σ CCl * shape resonance in 5-chlorouracil. Exploratory calculations performed at selected C–Cl bond lengths suggest that the \documentclass[12pt]{minimal}\begin{document}$\sigma _{\rm CCl}^*$\end{document}σ CCl * resonance could couple to the two lowest π* 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.

Uracil

Sigma

Shape resonance

Branching (polymer chemistry)

10.1063/1.4861589

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Citations (59)