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Elastic, vibrational and rotational cross sections for positron scattering from molecular oxygen are reported within the close-coupling formalism, using a three-dimensional positron–target potential energy surface. The present elastic values show good agreement with a recently reported theoretical prediction and helps to better understand the observed discrepancies between theory and experiment for energies below 1 eV . For energies up to the opening of the positronium channel, details of the elastic cross section are also discussed. The cross section for excitation of the fundamental vibrational mode shows a sharp onset at threshold followed by a peak, similar to the observed in our previous work for the N 2 target, although roughly three times greater than the last one. The rotational excitation cross sections for positron scattering from O 2 are reported. [ABSTRACT FROM AUTHOR]

Partial ionization cross section (PICS) measurements of the cations created through electron impact in the energy range from threshold ionization to 100 eV have been undertaken for 38 cations of 2-butanol, using a HIDEN quadrupole mass spectrometer (EPIC 300) with a mass resolution of 1 amu. These PICSs, which are being presented here for the first time, correspond to the cationic fragments with the highest intensity signal registered in our 2-butanol mass spectrum reported previously (Amorim et al. in Eur J Phys D 76:207, 2022). Experimental and theoretical total ionization cross sections (TICSs) for the electron impact of 2-butanol are also reported here, where the agreement between measured and calculated TICS over their common energy regimes was, allowing for the measurement uncertainties, typically quite good. Based on the previously reported appearance energy values and the PICSs profiles reported here, we propose some ionic fragmentation mechanisms for this molecule. [ABSTRACT FROM AUTHOR]

Integral, differential and momentum-transfer elastic cross sections for the scattering of low-energy electrons by hydrogen peroxide (HP), dimethyl peroxide (DMP) and ethylene glycol (ETG) are reported. These cross sections were calculated in the static-exchange and static-exchange plus polarization approximations for energies up to 30 eV by using the Schwinger multichannel method implemented with norm-conserving pseudopotentials. Through the symmetry decomposition of the integral cross section according to the C 2 h point group and the diagonalization of the scattering Hamiltonian, shape resonances were assigned to all three molecules. One shape resonance, namely σ OO ∗ of B u symmetry, was observed for HP around 2.5 eV. Due to the elongation of the O–O bond, when methyl groups are added to HP to form DMP, this resonance is shifted toward 2.1 eV in the DMP integral cross section. For DMP and ETG, a second peak, a broad structure that originates from the superposition of shape resonances of A g , A u and B u symmetries, was observed for higher impact energies. By comparing the cross sections of DMP and ETG, we found that the most striking differences appear in the low-energy regime, while for higher impact energies the cross sections are very similar, as expected for isomers. [ABSTRACT FROM AUTHOR]

The Siegert relation relates field and intensity temporal correlations. After a historical review of the Siegert relation and the Hanbury Brown and Twiss effect, we discuss the validity of this relation in two different domains. We first show that this relation can be used in astrophysics to determine the fundamental parameters of stars, and that it is especially important for the observation with stellar emission lines. Second, we check the validity of this relation for moving quantum scatterers illuminated by a strong driving field. [ABSTRACT FROM AUTHOR]

In this work, the mass spectrum (MS) and the appearance energies (AEs) of the ionic fragments formed in the collisions of electrons with 2-butanol were studied using a HIDEN—EPIC300 mass spectrometer. The MS was acquired for the electron impact energy of 70 eV, in the mass region of 1–75 amu and with a mass resolution of 1 amu. Here we observed the formation of 51 cationic fragments, which is a significant extension to the data previously reported in the literature. The relative abundances of the registered peaks in the MS compare reasonably well with the available values reported in the literature, where such a comparison can be made. The AEs were determined from the acquisition of ionic fragmentation curves of 2-butanol, for the electron impact energies covering the region of the ionic fragment formation threshold up to about ten eV above that value. The extended Wannier law was applied to obtain the AEs and Wannier exponents (p) of the fragments recorded in the MS, with relative intensities typically > 0.5% of the most intense fragment. This yielded data for 38 fragments, for which data of 30 of those fragments are reported for the first time in this work. [ABSTRACT FROM AUTHOR]

We present a study of low energy electron- N 2 scattering, with focus on vibrational excitations. Differential excitation cross sections are calculated using the multichannel version of the continued fractions method in the body-frame vibrational close-coupling scheme for the incident energy below 15 eV . The electron-molecule interaction potential is treated in the static-exchange-polarization-correlation approximation, where the exchange interaction is treated exactly. The results are compared with experimental data available in the literature. [ABSTRACT FROM AUTHOR]

We report a theoretical investigation on low-energy electron scattering by cubane ( C 8 H 8 ) molecules. Theoretical elastic differential, integral and momentum transfer cross sections are calculated at impact energies up to 20 eV. The calculations employed the Schwinger multichannel method implemented with norm-conserving pseudopotentials and were carried out in the static-exchange and static-exchange plus polarization approximations. Our results are compared with previous electron transmission spectroscopy data and integral cross sections obtained from a model potential calculation. Present calculations displayed three resonances, centered at 3.2, 6.6 and 11 eV, a Ramsauer–Townsend minimum at 0.16 eV, and the evidence of a virtual state. A set of differential elastic cross sections for electron–cubane collisions is presented here for the first time. Electronic structure calculations were performed in order to help with the interpretation of the low-energy resonance. [ABSTRACT FROM AUTHOR]

We explore a theoretical model that goes beyond the Standard Model Extension with the purpose of studying nonrelativistic quantum effects associated with a privileged direction in the spacetime. The existence of a privileged direction in the spacetime is a hypothesis made by assuming the violation of the Lorentz symmetry through a fixed vector field. Then, we search for Lorentz symmetry violation effects around a long non-conductor cylinder. We analyze the possibility of achieving bound states and also finding a lower bound for the parameters of the Lorentz symmetry violation. [ABSTRACT FROM AUTHOR]

Benzene is undoubtedly one of the most studied target molecules in electron scattering experiments and calculations. However, there is still a huge knowledge gap on the electronic excitation cross sections of this fundamental collision. Here, we report calculated differential and integral cross sections for elastic and electronic excitation, as well as total cross sections, for electron scattering by the benzene molecule, for impact energies in the 10–50 eV range. We have employed the Schwinger multichannel method, in two levels of approximation. By including extra diffuse functions in the second calculation, the role of higher lying Rydberg states in the multichannel coupling scheme was assessed. We found that such states have minor effects on the elastic and total cross sections. In contrast, the electronic excitation cross sections of the lower-lying bands decrease in magnitude when accounting for the higher Rydberg states, and this effect becomes more pronounced at lower impact energies. Our computed elastic cross sections are in quite good agreement with the available experimental data, whereas the comparison for the electronic excitation channels is still satisfactory. We also discuss the need for accurate excitation energies in order to properly compare theoretical and experimental electronic excitation cross sections. [ABSTRACT FROM AUTHOR]

We propose a model potential for computing total ionization cross sections for atoms and molecules by electron impact. The potential is obtained by a fitting procedure using the Binary–Encounter–Bethe model cross sections as a starting point. We present total ionization cross section for hydrogen, carbon, nitrogen and oxygen atoms and for hydrogen, nitrogen, water, methane and benzene molecules. The results obtained with our model potential are compared with results obtained with the Binary–Encounter–Bethe model and with the first Born approximation, and agreement is quite good. Our results show that this potential could be used to account for the ionization channel in an electron–molecule collision calculation. [ABSTRACT FROM AUTHOR]

We report elastic, electronically inelastic, total ionization and total cross sections for the scattering of electrons by trans-formic acid. The calculations of the elastic and electronically inelastic cross sections were performed with the Schwinger multichannel method implemented with norm-conserving pseudopotentials. The electronically inelastic calculations were done within the minimal orbital basis for single configuration interaction approach with different multichannel coupling schemes considering from 1 up to 51 open channels, which enable us to study the influence of the multichannel coupling effects on the calculated cross sections. Polarization effects in the elastic channel were taken into account considering only the excitations related to the pairs used in the minimal orbital basis for single configuration interaction approach. We found that the magnitude of the elastic and inelastic cross sections decreases as more channels are treated as open in the scattering calculations. The calculated elastic differential cross sections present an overall good agreement with previous studies found in the literature. The elastic integral cross section presents a well-known π ∗ shape resonance centered at 1.96 eV. The total ionization cross section was calculated with the binary-encounter-Bethe model and presents a good agreement with previous results from the literature. The total cross section was estimated using the calculated elastic, inelastic and ionization cross sections. [ABSTRACT FROM AUTHOR]

From the interaction of the magnetic quadrupole moment of the neutral particle with magnetic and electric fields, we analyse the appearance of attractive Coulomb-type potentials. In addition, based on the field configurations that produce the Coulomb-type potentials inside a long conductor cylinder and a long nonconductor cylinder, we discuss how a cut-off point can arise from. Then, we analyse the influence of the cut-off point on the Coulomb-type potentials by searching for bound states. [ABSTRACT FROM AUTHOR]

We have investigated the relativistic quantum dynamics of a scalar field in an anisotropic background governed by the Lorentz symmetry violation. This analysis is done through a non-minimal coupling in the Klein–Gordon equation, which is inspired by the CPT-odd gauge sector of the standard model extension. From the elaboration of a vector and electromagnetic field configuration as a possible Lorentz break scenario, we induced an electric field which influences the scalar field. In this scenario, we show that it is possible to determine two energy profiles for the system, that is, a description of the relativistic quantum dynamics of the scalar field in the xy-plane and in all space-time. [ABSTRACT FROM AUTHOR]

We report a theoretical–experimental investigation on elastic electron scattering by acetaldehyde (CH 3 CHO) in the 0.5–800 eV energy range. Theoretically, the Padé approximation and the single-center partial-wave expansion method were applied to solve the Lippmann–Schwinger scattering equation, whereas a molecular complex optical potential was used to describe the electron–molecule interaction. Calculations in the independent-atom framework were also performed. Angular distributions of the elastically scattered electrons were measured in the 10 ∘ –130 ∘ and 30–800 eV ranges using a crossed beams geometry. Absolute values of differential cross sections were derived by the relative flow technique. In addition, integral and momentum transfer cross sections were obtained from the experimental and theoretical differential cross sections via a numerical integration procedure. Comparison between our results and previous experimental and theoretical calculations is made. [ABSTRACT FROM AUTHOR]