Excitation Cross Sections Research Articles

Low energy electron induced chemistry for e-bromine molecule scattering

The present study focuses on electron collision with bromine molecule, employing ab-initio scattering calculations. Using the R-matrix method, we calculated elastic and inelastic cross-sections using two different scattering models: static exchange with polarization and close-coupling. Our findings reveal total three low energy resonances for e-Br2 scattering which are primarily formed through transient negative ions. This observation is supported by dissociative electron attachment cross-section analysis, potential energy curves, and molecular orbital diagrams. Out of these three, first is at zero-energy, the electron attachment is recognized as shape-resonance and further two π* resonances as core-excited resonances. Present computation becomes more important as many cross-sections are reported as bench mark results in absence of any reported data. For instance: elastic, differential, momentum transfer, excitation and total cross-section. Comparing our results with sparse existing literature, we find good agreement.

The Excitation of the 3D and 4D States of Atomic Hydrogen by Electron Impact

The excitation cross-sections of the 3D and 4D states of atomic hydrogen at low incident energies (from 0.90 to 5.00 Ry) were calculated using the variational polarized orbital method, which is also called the hybrid theory. Up to 12 partial waves (L = 2 to 13) were used to obtain converged cross-sections at high energies. The importance of the long-range forces near the threshold region and the behavior of the cross-sections in that region are indicated. The S, P, and D cross-sections are needed if the total excitation cross-sections are measured in addition to the elastic cross-sections. These cross-sections are also useful if the cascade from the D to the P to the S states is considered in the diagnostics of solar and astrophysical observations.

Atomic collisional data for neutral beam modeling in fusion plasmas

The injection of energetic neutral particles into the plasma of magnetic confinement fusion reactors is a widely-accepted method for heating such plasmas; various types of neutral beam are also used for diagnostic purposes. Accurate atomic data are required to properly model beam penetration into the plasma and to interpret photoemission spectra from both the beam particles themselves (e.g. beam emission spectroscopy) and from plasma impurities with which they interact (e.g. charge exchange recombination spectroscopy). This paper reviews and compares theoretical methods for calculating ionization, excitation and charge exchange cross sections applied to several important processes relevant to neutral hydrogen beams, including H + Be4+ and H + H+. In particular, a new cross section for the proton-impact ionization of H (1s) is recommended which is significantly larger than that previously accepted at fusion-relevant energies. Coefficients for an empirical fit function to this cross section and to that of the first excited states of H are provided and uncertainties estimated. The propagation of uncertainties in this cross section in modeling codes under JET-like conditions has been studied and the newly-recommended values determined to have a significant effect on the predicted beam attenuation. In addition to accurate calculations of collisional atomic data, the use of these data in codes modeling beam penetration and photoemission for fusion-relevant plasma density and temperature profiles is discussed. In particular, the discrepancies in the modeling of impurities are reported. The present paper originates from a Coordinated Research Project (CRP) on the topic of fundamental atomic data for neutral beam modeling that the International Atomic Energy Agency (IAEA) ran from 2017 to 2022; this project brought together ten research groups in the fields of fusion plasma modeling and collisional cross section calculations. Data calculated during the CRP is summarized in an and is available online in the IAEA’s atomic database, CollisionDB.

Theoretical investigations of positron collisions with phosphorus-containing compounds

A theoretical investigation of positron scattering from phosphorus-containing compounds (viz., PH3, P2H4, PCl3, PF3, PBr3, POF3, POCl3, and H2PO4) is reported in this article. The quantum mechanical potential scattering approach is utilized to calculate integral elastic, excitation, momentum transfer, direct ionization, positronium formation, total ionization, inelastic, differential, and total cross sections on a fine energy grid from 1 to 5000 eV. The ionization contribution in the inelastic scattering is estimated using the complex scattering potential-ionization contribution technique. Prior research on positron collisions with these targets is scarce; as a result, the purpose of this study is to make up, at least in part, for this deficiency in cross-section data. In addition to being pertinent to positron transport analyses, such as Monte Carlo methods, the current results should be useful to benchmark the accuracy and validity of positron molecule collision computations and, more significantly, to compare these calculations with related electron scattering outcomes. Furthermore, the calculated cross sections of PH3 are compared with NH3 and other phosphorus-containing compounds. The analysis makes it abundantly evident that the atoms on the periphery of a molecule have a substantially larger impact on the scattering process than the central atom. To analyze the scattering dynamics of positrons and their anti-particle electrons, a comparative study of cross sections of H2PO4 and H2SO4 is also presented. For most of these targets, positron calculations are carried out for the first time.

An improved artificial neural network fit of the ab initio potential energy surface points for HeH+ + H2 and its ensuing rigid rotors quantum dynamics

Artificial neural networks (ANN) have been shown for the last several years to be a versatile tool for fitting ab initio potential energy surfaces. We have demonstrated recently how a 60-neuron ANN could successfully fit a four-dimensional ab initio potential energy surface for the rigid rotor HeH+ - rigid rotor H2 system with a root-mean-squared deviation (RMSD) of 35 cm−1. We show in the present study how a (40, 40) neural network with two hidden layers could achieve a better fit with an RMSD of 5 cm−1. Through a follow-up quantum dynamical study of HeH+(j1)-H2(j2) collisions, it is shown that the two fits lead to slightly different rotational excitation and de-excitation cross sections but are comparable to each other in terms of magnitude and dependence on the relative translational energy of the collision partners. When averaged over relative translational energy, the two sets of results lead to rate coefficients that are nearly indistinguishable at higher temperatures thus demonstrating the reliability of the ANN method for fitting ab initio potential energy surfaces. On the other hand, we also find that the de-excitation rate coefficients obtained using the two different ANN fits differ significantly from each other at low temperatures. The consequences of these findings are discussed in our conclusions.

Oscillator Strengths and Cross Sections of the Valence-Shell Excitations of HBr Studied by Fast Electron Impact.

The oscillator strengths and cross sections of the valence-shell excitations of HBr were determined by fast electron scattering with an incident electron energy of 1500 eV and an energy resolution of 80 meV. The momentum transfer dependence behaviors of the generalized oscillator strengths have been used to elucidate the transition characteristics. The present results show that the strong spin-orbital interaction results in the observation of some triplet states in the (Λ, S) coupling and the constant generalized oscillator strength ratios for the pair states with the same electronic configuration and quantum number Ω, and the quantitative spin-orbit coupling coefficients of b3Π1(v = 0) and C1Π(v = 0) are determined. The optical oscillator strengths of the valence-shell excitations were obtained by extrapolating the generalized oscillator strengths to the limit of zero squared momentum transfer. The present optical oscillator strengths give an independent cross-check of the previous experimental and theoretical results, and the comparison shows that the line-saturation effect is more severe for the high Rydberg states with large intensities and narrow natural widths. The integral cross sections of the valence-shell excitations of HBr were obtained from the excitation threshold to 5000 eV by the BE-scaling method. The present oscillator strengths and cross sections supplement the fundamental molecular database of HBr and can be used for modeling in the semiconductor industry, astrophysics, and atmospheric chemistry.

Enhanced the yellow emission of Dy3+/Eu3+: Na5Lu9F32 fluoride single crystals by the introduction of inactive central Y3+ ions

High-quality Na5Lu9F32 single crystals incorporated with Dy3+, Dy3+/Eu3+, and Dy3+/Eu3+/Y3+ ions were successfully synthesized by a reformative Bridgman technique. A significantly enhanced 573nm yellow emission for the Dy3+/Eu3+ incorporated crystal by dopant of inactive central Y3+ ions was demonstrated upon excitation of 453nm. The broken of the Dy3+ clusters by addition of Y3+ dopant was probably the main reason for the enhancement of the yellow emission. The crystal still held the phase of Na5Lu9F32 although the doping level reaches to 1.5 mol% Y3+ while the peaks of X-ray diffraction (XRD) were slightly blue-shifted, and Y3+ ions replaced the Lu3+ lattices as consequence of Rietveld structure refinements of the crystals. The maximum excited absorption and emission cross-sections at 573nm were also computed to be ∼8.91×10−21 and ∼6.06×10−21 cm2 separately. Therefore, the Dy3+/Eu3+/Y3+ tri-doped Na5Lu9F32 single crystal was considered as a prospective yellow solid-state laser material for related optical devices.

Oscillator strength and cross section study of the valence-shell excitations of NO2 by fast electron scattering

Abstract Oscillator strengths and cross sections of the valence-shell excitations in NO2 are of great significance in testing the theoretical calculations and monitoring the state of ozone layer in the earth’s atmosphere. In the present work, the generalized oscillator strengths of the valence-shell excitations in NO2 were obtained based on the fast electron scattering technique at an incident electron energy of 1.5 keV and an energy resolution of about 70 meV. By extrapolating the generalized oscillator strengths to the limit of a zero squared momentum transfer, the optical oscillator strengths for the dipole-allowed transitions have been obtained, which provide an independent cross check to the previous experimental results. Based on the BE-scaling method, the corresponding integral cross sections have also been derived systematically from the excitation threshold to 5000 eV. The present dynamic parameters can provide the fundamental spectroscopic data of NO2 and have important applications in the studies of atmospheric science.Oscillator strengths and cross sections of the valence-shell excitations in NO2 are of great significance in testing the theoretical calculations and monitoring the state of ozone layer in the earth’s atmosphere. In the present work, the generalized oscillator strengths of the valence-shell excitations in NO2 were obtained based on the fast electron scattering technique at an incident electron energy of 1.5 keV and an energy resolution of about 70 meV. By extrapolating the generalized oscillator strengths to the limit of a zero squared momentum transfer, the optical oscillator strengths for the dipole-allowed transitions have been obtained, which provide an independent cross check to the previous experimental results. Based on the BE-scaling method, the corresponding integral cross sections have also been derived systematically from the excitation threshold to 5000 eV. The present dynamic parameters can provide the fundamental spectroscopic data of NO2 and have important applications in the studies of atmospheric science.

Electron-impact Excitation of Pt i–iii: The Importance of Metastables and Collision Processes in Neutron Star Merger and Laboratory Plasmas

The detection of a gravitational-wave signal and subsequent electromagnetic transient from a neutron star merger in 2017 is consistent with expectations of neutron star mergers as an r-process element production site. Within the first few days post-merger, the kilonova spectra are consistent with a blackbody illuminating a mix of heavy, r-process elements. With increasing time, the kilonova transitions to the non-LTE regime where the level populations and ionization balance are determined by both collisional and photoprocesses. Detailed cross section data for electron-impact processes involving the relevant species are often not available. In such circumstances, it is reasonable to use approximate methods as baseline data for use in spectral modeling, and it is useful to evaluate the accuracy of such methods against more sophisticated collision calculations when possible. We describe new calculations of the electron-impact excitation cross sections of Pt i–iIi using the DARC R-matrix codes. Using collisional-radiative models, we show that, at plasma conditions expected in kilonovae, the expressions of van Regemorter and Axelrod are insufficient for producing electron-impact excitation data for complex, heavy species such as the low charge states of Pt. Through comparisons with data generated with the relativistic distorted wave approach, as implemented in the Flexible Atomic Code, we show the distorted wave method produces cross section data that, when incorporated into spectral models, predicts strong spectral feature distributions similar in intensity to those from models built on data computed with the R-matrix approach for the considered ions and plasma conditions.

Calculation of Ionization, Excitation and Electron Capture Cross Sections for Be4+ + H(2s,2p) Collisions.

A computational study of Be4+ + H(2s,2p) collisions has been carried out employing the Classical Trajectory Monte Carlo (CTMC) method for the impact energy range from 20 keV/u to 1000 keV/u. The integral n partial cross sections for H(n) excitation and Be3+(n) electron capture and, the total ionization and electron capture cross sections are calculated and compared to recent semiclassical results. A general good agreement is observed for the n partial and total electron capture and ionization cross sections. The comparative study of the three inelastic processes show no significant differences between both excited targets.

An effective method to calculate the electron impact excitation cross sections of helium from ground state to a final channel in the whole energy region

The electron impact excitation (EIE) cross sections of an atom/ion in the whole energy region are needed in many research fields, such as astrophysics studies, inertial confinement fusion researches and so on. In the present work, an effective method to calculate the EIE cross sections of an atom/ion in the whole energy region is presented. We use the EIE cross sections of helium as an illustration example. The optical forbidden 1 1S–n 1S (n = 2–4) and optical allowed 1 1S–n 1P (n = 2–4) excitation cross sections are calculated in the whole energy region using the scheme that combines the partial wave R-matrix method and the first Born approximation. The calculated cross sections are in good agreement with the available experimental measurements. Based on these accurate cross sections of our calculation, we find that the ratios between the accurate cross sections and Born cross sections are nearly the same for different excitation final states in the same channel. According to this interesting property, a universal correction function is proposed and given to calculate the accurate EIE cross sections with the same computational efforts of the widely used Born cross sections, which should be very useful in the related application fields. The datasets presented in this paper are openly available at https://www.doi.org/10.57760/sciencedb.j00113.00142.

Electron impact fine-structure cross-section calculations of Cu and their applications in the diagnostics of laser-produced Cu-plasma through the collisional radiative model

We present the calculations of electron impact excitation cross-sections for the transitions from the ground state of Cu 3d104sS1/22 to the excited fine structure energy levels of the configurations 3d94s2,3d94s4p,3d104l,(l=p,d,f),3d105l,(l=s,p,d),3d10nl,(n=6,7;l=s,p) using the fully relativistic distorted wave theory. In addition, cross-sections for the transitions from the metastable states 3d94s2D5/2,3/22 to the upper excited levels are also presented. For calculating these cross-sections, we have obtained the atomic wave functions of copper using the multi-configuration Dirac–Fock approximation theory. To ensure the accuracy of these wave functions, we compared our calculated oscillator strengths of some dipole-allowed transitions of Cu with the available earlier reported values. We have utilized all the calculated electron impact fine-structure level excitation cross-sections from the ground as well as the metastable states of Cu to develop a fine structure-resolved collisional-radiative (CR) model for the diagnostics of laser-produced Cu plasma at atmospheric pressure. The model has been applied for diagnostics by coupling it with the spatially resolved optical emission spectroscopy (OES) measurements of Singh and Sharma [Phys. Plasmas 23 122104 (2016)] in the presence and absence of a static magnetic field. For diagnostics, the intensities of three OES observed strong atomic emission lines of Cu viz, 510.5, 515.3, and 521.8 nm have been utilized in the absence and presence of a magnetic field at different axial lengths (z = 0.5–6.5 mm) from the Cu target. Also, these intensities are corrected using the internal reference self-absorption method to overcome the effect of radiation trapping. The normalized intensities of the considered lines obtained from the CR model have been compared with their corresponding OES-measured values to extract the plasma parameters, i.e., electron temperature and electron density. Further, the obtained electron temperatures from the CR model are compared with the corresponding values reported in the experimental paper of Singh and Sharma [Phys. Plasmas 23 122104 (2016)] obtained using the Boltzmann plot method.

Calculation of electronic excitation cross sections and rate coefficients for boron monohydride (BH)

Aiming at the quantitative diagnostics of boron monohydryde, BH, in fusion plasmas, we present elastic, electronic excitation, and ionization cross sections of BH for the first time. The calculations were performed by the R-matrix and Born Encounter Bethe methods utilized by Quantemol-EC software. To examine the uncertainty due to the calculation conditions, we compared the results by different basis sets and internuclear distances of the target model. We found that the uncertainties are typically within ∼10%. Rate coefficients were derived and fitted to an Arrhenius function. The derived decay rate per photon, , agreed with the value presented by Lieder et al (the ASDEX-Upgrade Team) (1994 Eur. Phys. Soc. Conf. Plasma Phys. 2 722).

Measurement of three-photon excitation cross-sections of fluorescein from 1154 nm to 1500 nm.

Measurements of three-photon action cross-sections for fluorescein (dissolved in water, pH ∼11.5) are presented in the excitation wavelength range from 1154 to 1500 nm in ∼50 nm steps. The excitation source is a femtosecond wavelength tunable non-collinear optical parametric amplifier, which has been spectrally filtered with 50 nm full width at half maximum band pass filters. Cube-law power dependance is confirmed at the measurement wavelengths. The three-photon excitation spectrum is found to differ from both the one- and two-photon excitation spectra. The three-photon action cross-section at 1154 nm is more than an order of magnitude larger than those at 1450 and 1500 nm (approximately three times the wavelength of the one-photon excitation peak), which possibly indicates the presence of resonance enhancement.

Calculated cross sections for electron collisions with the BeN molecule

We report a low energy electron collision calculation with the BeN molecule in its X ground state using the molecular R-matrix method at a single geometry, namely, the equilibrium a 0 of the molecule. Using a suitable target model, we have calculated the elastic cross section and cross sections for electron impact excitation in several low-lying excited states of BeN. Cross sections for electron impact dissociation is derived from the electronic excitation cross sections. In addition, molecular data on bound sates of BeN and e-BeN negative ion resonances and widths at the target equilibrium Re that may be relevant for other studies are also provided.

Experimental and BEf-scaled cross sections for electron-impact excitation of ammonia molecules from near threshold to high-intermediate energy

Experimental and BEf-scaled cross sections for electron-impact excitation of ammonia molecules from near threshold to high-intermediate energy

Relativistic calculation of electron impact excitation of tin: cross sections of importance in plasma modeling

The present work includes the calculation of electron impact excitation cross sections for the fine structure resolved transitions in Sn I and Sn II, using the relativistic distorted wave approximation with the aid of Dirac-Fock multiconfigurational wavefunctions. For Sn I, the cross sections are calculated for the excitations from the fine structure resolved energy levels of the manifolds, , , , and including the ground state, to the fine structure resolved levels of , , , , and manifolds for a wide range of projectile electron energy from 0 to 500 eV. Further, the cross sections are also calculated for the excitations of Sn II from the fine structure resolved energy levels of the manifolds, , , , and including the ground state, to the fine structure resolved levels of , , , , and manifolds. All the cross sections for Sn I except for the excitation from the ground state to the fine-structure resolved excited states of , and manifolds and all the cross sections for Sn II are reported for the first time. In order to ensure the consistency of the present calculations, a comparison of the oscillator strengths and transition probabilities is carried out with the available calculations and measurements. The present cross sections are also compared with previous calculations and observed to be in reasonable agreement. The calculated cross sections are of great interest in the modeling and diagnostic of various plasmas such as laser induced plasma, fusion plasma, etc. Further, to ease the use of calculated cross sections, the analytic fitting of the cross sections is also provided.

The density and pressure of helium nano-bubbles encapsulated in silicon

The 1 s 2 → 1 s 2 p ( 1 P ) excitation in compressed helium atoms in either the bulk material or encapsulated in a bubble is shifted to energies higher than in the free atom. For bulk helium, energy shifts predicted from non-empirical electronic structure computations are in excellent agreement with experimentally determined values. However, there are significant discrepancies both between the results of experiments on different bubbles and between these and the well established descriptions of the bulk. A critique is presented of previous analyses of earlier scanning transmission electron microscope measurements that are untrustworthy because the density dependence of the electron impact excitation cross section was neglected. Experimental electron energy loss data from an earlier study of helium encapsulated in silicon are reanalysed and it is shown that the properties of the helium in these bubbles do not differ significantly from those in the bulk, thereby enabling the densities in the bubbles to be determined. These enable bubble pressures to be deduced from a well established experimentally derived equation of state. It is shown that the errors of up to 80% in the incorrectly determined densities are greatly magnified in the predicted pressures which can be too large by factors of over seven.

Theory of isomeric excitation of 229Th via electronic processes

A unified theoretical framework is presented for the isomeric excitation of the 229Th nucleus via electronic processes. These processes include nuclear excitation by electron transition (NEET), nuclear excitation by electron capture (NEEC), and nuclear excitation by inelastic electron scattering (NEIES). Detailed calculation results on the excitation rate and the excitation cross section are presented.

PO+−He collision: ab initio potential energy surface and inelastic rotational rate coefficients

ABSTRACT Computations involving quantum dynamics are performed to attain cross-sections corresponding to rotational de-excitation and excitation rates of the PO+ species including four rotational lines recently detected in the interstellar molecular clouds. New ab initio potential energy surface (PES) for PO+−He collision is constructed by using CCSD(T) method and basis set extrapolated to complete basis set limit (CBS) considering a rigid rotor approximation. The PES is then trained to create neural network (NN) model to construct an augmented surface with angular coordinates at 1° intervals. The PES has a global minimum located at $\theta =110{}^{\circ }$ and R = 3.1 Å. An analytical fitting is performed on the NN surface to obtain the first 41 radial coefficients needed to solve the equations of the coupled-channel method. The essentially precise close coupling approach is used to compute the rotational (de-)excitation cross-sections till 1400 cm−1 with rotational states converged up to 26. Further, these cross-sections are thermally averaged to get the rate coefficients for various rotational transitions till 200 K. The propensity rule favours the odd transitions (Δj = 1) for the current study. The rate for the transition 5 → 4 is found to be higher than transition 1→ 0 by a factor of 3.1 at T = 20 K that decreases to 2.1 at T = 100 K.