Absolute Total Cross Sections Research Articles

Unveiling the electron-induced ionization cross sections and fragmentation mechanisms of 3,4-dihydro-2H-pyran.

The interactions of electrons with molecular systems under various conditions are essential to interdisciplinary research fields extending over the fundamental and applied sciences. In particular, investigating electron-induced ionization and dissociation of molecules may shed light on the radiation damage to living cells, the physicochemical processes in interstellar environments, and reaction mechanisms occurring in combustion or plasma. We have, therefore, studied electron-induced ionization and dissociation of the gas phase 3,4-dihydro-2H-pyran (DHP), a cyclic ether appearing to be a viable moiety for developing efficient clinical pharmacokinetics and revealing the mechanisms of biofuel combustion. The mass spectra in the m/z = 10-90 mass range were measured at several different energies of the ionizing electron beam using mass spectrometry. The mass spectra of DHP at the same energies were simulated using on-the-fly semi-classical molecular dynamics (MD) within the framework of the QCxMS formalism. The MD settings were suitably adjusted until a good agreement with the experimental mass spectra intensities was achieved, thus enabling a reliable assignment of cations and unraveling the plausible fragmentation channels. Based on the measurement of the absolute total ionization cross section of DHP (18.1 ± 0.9) × 10-16cm2 at 100eV energy, the absolute total and partial ionization cross sections of DHP were determined in the 5-140eV electron energy. Moreover, a machine learning algorithm that was trained with measured cross sections from 25 different molecules was used to predict the total ionization cross section for DHP. Comparison of the machine learning simulation with the measured data showed acceptable agreement, similar to that achieved in past predictions of the algorithm.

Absolute partial and total ionization cross sections of carbon monoxide with electron collision from 350 eV to 8000 eV

The absolute partial and total cross sections for electron impact ionization of carbon monoxide are reported for electron energies from 350 eV to 8000 eV. The product ions (CO+, C+, O+, CO2+, C2+, and O2+) are measured by employing an ion imaging mass spectrometer and two ion-pair dissociation channels (C+ + O+ and C2+ + O+) are identified. The absolute cross sections for producing individual ions and their total, as well as for the ion-pair dissociation channels are obtained by normalizing the data of CO+ to that of Ar+ from CO–Ar mixture target with a fixed 1:1 ratio. The overall errors are evaluated by considering various kinds of uncertainties. A comprehensive comparison is made with the available data, which shows a good agreement with each other over the energy ranges that are overlapped. This work presents new cross-section data with electron energies above 1000 eV.

Electron Scattering from Methyl Formate (HCOOCH3): A Joint Theoretical and Experimental Study.

Elastic low-energy electron collisions with methyl formate have been studied theoretically at the level of various theories. The elastic integral cross section was calculated using Schwinger multichannel and R-matrix methods, in the static-exchange and static-exchange plus polarization levels of approximations for energies up to 15 eV. The absolute total cross section for electron scattering from methyl formate has been measured in a wide energy range (0.2-300 eV) using a 127° electron spectrometer working in the linear transmission configuration. The integral elastic and the absolute total cross sections display a π* shape resonance at around 1.70-1.84 eV, which can be related to the resonance visible for formic acid, and a broad structure located at 7-8 eV, which can be associated to a superposition of σ* shape resonances. Our results were compared with theoretical and experimental results available in the literature and with the results of electron collisions with formic acid. The additivity rule was used to estimate the total cross section of methyl formate and the results agree well with the experimental data.

Measurement of the Charge Exchange Cross Section for N7+, O7+ Ions in Collision with Atomic H

The absolute total cross sections for the charge exchange between highly charged ions 15N7+, O7+, and atomic H have been measured with the ion-atom merged-beams apparatus at Oak Ridge National Laboratory. The collision energy range is from 1224 down to 2 eV u−1, which covers outflowing hot components of astrophysical charge exchange plasmas like stellar-wind and supernova remnants. Good agreement with the previous measurements and theory is found for the collision energies above 100 eV u−1, while below 100 eV u−1 limited agreement is achieved with the available calculations. These cross-section data are useful for modeling X-ray emission resulting from the charge exchange at the interface of hot plasma interacting with ambient neutral gas.

Photoionisation of the CH radical using the B-spline R-matrix method

Aims. The primary motivation for this paper is to provide accurate data for the photoionisation of the CH radical, including the absolute total photoionisation cross-section, partial cross-sections, and photoelectron angular distribution. In addition, the near threshold features in the photoionisation curve (which are absent in previous studies) are produced with high precision. Methods. A multichannel wavefunction based on the R-matrix approach, which uses the configuration interaction (CI) method to describe electronic correlation, is carried out in the present calculations. A set of B-spline orbitals is employed to represent the accurate continuum. The distinctive feature of the present calculations allows us to generate a more accurate description of the bound and continuum states than those employed before. Results. Total photoionisation cross-sections from the ground state of CH radicals and partial cross-sections corresponding to 1π, 3σ, and 2σ states of CH+ ions are presented for photon energies ranging from threshold to 80 eV. Extensive resonance structures, which are absent in previous studies, are observed for the first time near the ionisation threshold. The cross-section dataset obtained from the present calculations is expected to be sufficiently accurate and comprehensive for most current modelling applications involving the photon and CH radical scattering system.

Medium effects in antikaon-induced Ξ− hyperon production on nuclei near threshold

We study the antikaon-induced inclusive cascade Ξ− hyperon production from 12C and 184W target nuclei near threshold within a nuclear spectral function approach. The approach describes incoherent direct Ξ− hyperon production in elementary K−p→K+Ξ− and K−n→K0Ξ− processes as well as takes into account the influence of the scalar nuclear K−, K+, K0, Ξ− and their Coulomb potentials on these processes. We calculate the absolute differential and total cross sections for the production of Ξ− hyperons off these nuclei at laboratory angles ≤ 45∘ by K− mesons with momenta of 1.0 and 1.3 GeV/c, which are close to the threshold momentum (1.05 GeV/c) for Ξ− hyperon production on the free target nucleon at rest. We also calculate the momentum dependence of the transparency ratio for the 184W/12C combination for Ξ− hyperons at these K− beam momenta. We show that the Ξ− differential and total (absolute and relative) production cross sections at the considered initial momenta reveal a distinct sensitivity to the variations in the scalar Ξ− nuclear potential at saturation density ρ0, studied in the paper, in the low-momentum region of 0.1–0.6 GeV/c. We also demonstrate that for the subthreshold K− meson momentum of 1.0 GeV/c there is, contrary to the case of its above threshold momentum of 1.3 GeV/c, a strong sensitivity of the transparency ratio for Ξ− hyperons to the considered changes in the Ξ− nuclear potential at all outgoing Ξ− momenta as well, which cannot be masked, as in the case of differential and total observables mentioned above, by that associated with the possible changes in the poorly known experimentally Ξ−N inelastic cross section. Therefore, the measurement of these absolute and relative observables in a dedicated experiment at the J-PARC Hadron Experimental Facility will provide valuable information on the Ξ− in-medium properties, which will be complementary to that deduced from the study of the inclusive (K−,K+) reactions at incident momenta of 1.6–1.8 GeV/c in the Ξ− bound and quasi-free regions.

Absolute cross sections and asymmetry parameters for photodetachment of C−(4So)

Absolute total cross sections and asymmetry parameters for the photodetachment of the ${}^{4}{S}^{o}$ ground state of ${\mathrm{C}}^{\ensuremath{-}}$ are reported for photon energies ranging from threshold to 6 eV. The total cross sections were measured using the animated crossed beam technique incorporating corrections for saturation, while the asymmetry parameters were obtained using velocity map imaging spectrometry. The measured values are in good agreement with theoretical results obtained from an $R$-matrix calculation using polarized pseudostates.

Antikaon-induced K1(1270)+ meson production on nuclei near threshold

We study the inclusive strange axial-vector meson K1(1270)+ production in K−A reactions at near-threshold laboratory incident antikaon momenta within a nuclear spectral function approach, which describes incoherent direct K1(1270)+ meson production in K− meson–proton K−p→K1(1270)+Ξ− production processes and accounts for three different options for its in-medium mass shift (or for its effective scalar potential) at central density ρ0. We calculate the absolute differential and total cross sections for the production of K1(1270)+ mesons on 12C and 184W target nuclei at laboratory angles of 0∘–45∘ by K− mesons with momenta of 2.5, 2.8 and 3.5 GeV/c, which are close to the threshold momentum (≈ 2.95 GeV/c) for K1(1270)+ meson production off the free target proton at rest. The intrinsic properties of carbon and tungsten target nuclei have been described in terms of their spectral functions, which take into account the momenta of target protons and the energies of their separation from the considered nuclei. We show that the differential and total (absolute and relative) K1(1270)+ antikaon-induced production cross sections at initial momenta not far from threshold – at momenta ∼ 2.8–3.5 GeV/c, at which there is yet no strong drop in their strength, reveal a distinct sensitivity to changes in the in-medium shift of the K1(1270)+ mass, studied in the paper, both in the K1(1270)+ meson low-momentum (0.1–1.0 GeV/c) and in its full-momentum ranges. This would permit evaluating this shift. Experimental data necessary for this aim can be obtained in a dedicated experiment at the J-PARC Hadron Experimental Facility.

Near-threshold K*(892)+ meson production in the interaction of π− mesons with nuclei

We study the inclusive production of strange vector mesons in reactions at near-threshold laboratory incident pion momenta of 1.4–2.0 GeV/c via a nuclear spectral function approach. The approach accounts for incoherent primary meson–proton production processes as well as the influence of the scalar –nucleus potential (or the in-medium mass shift) on these processes. We calculate the absolute differential and total cross sections for the production of mesons from carbon and tungsten nuclei at laboratory angles of 0 –45 and at the aforementioned momenta in five scenarios for the aforenoted shift. We show that the momentum distributions and their excitation functions (absolute and relative) possess a high sensitivity to changes in the in-medium mass shift in the low-momentum region of 0.1–0.6 GeV/c. Therefore, the measurement of such observables in a dedicated experiment at the GSI pion beam facility in the near-threshold momentum domain will allow us to get valuable information on the in-medium properties.

Acceptance-angle effects on the charge transfer and energy-loss cross sections for collisions ofC4+with atomic hydrogen

The charge-transfer process for collisions of ${\mathrm{C}}^{4+}$ with atomic hydrogen is studied theoretically and experimentally in this work. Our theoretical study is based on an electron-nuclear dynamics approach applied here for the state-to-state and total contributions to the electron-capture cross sections. Our theoretical results are complemented by experimental measurements of the absolute total cross section for collisions of ${\mathrm{C}}^{4+}$ with atomic hydrogen, which were carried out using an ion-atom merged-beams technique at relative collision energies of $0.122--2.756$ keV/u and performed with an improved apparatus at Oak Ridge National Laboratory. We find that the structure observed around a collision energy of 0.5 keV/u in the experimental results is due to the combined contributions of the $3\ensuremath{\ell}$ capture cross sections, the coupling of the electronic and nuclear dynamics, and the acceptance angle in the experimental configuration. We also report the ${\mathrm{C}}^{4+}$ kinetic energy loss and stopping cross section. We find that the ${\mathrm{C}}^{4+}$ gains energy for relative collision energies between 0.1 and 10 keV/u, with a maximum at $\ensuremath{\sim}1$ keV/u. Our theoretical study shows that, to compare to the merged-beams experimental results, one has to account for effects produced by the merged path length of the apparatus.

Absolute total cross sections of multiple electron processes for molecules of biological interest by fast proton impact

SynopsisWe present the study of multiple electron processes produced by impact of proton beams on molecular targets from intermediate to high projectile impact energies. Transition probabilities and absolute cross sections were determined by using the Continuum Distorted Wave-Eikonal Initial State approximation. Results were compared with previous calculations and also with recent experimental data.

Pion-induced production of Λ(1520) hyperons on nuclei near threshold

We study the pion-induced inclusive Λ(1520) hyperon production from nuclei near threshold within a nuclear spectral function approach accounting for incoherent primary π− meson–proton π−p→K0Λ(1520) production processes. We calculate the absolute differential and total cross sections for the production of Λ(1520) hyperons off carbon and tungsten nuclei at laboratory angles of 0∘–10∘, 10∘–45∘ and 45∘–85∘ by π− mesons with momentum of 1.7 GeV/c as well as their relative (transparency ratio) differential and integral yields from these nuclei within four scenarios for their total in-medium width. We demonstrate that these absolute observables, contrary to the relative ones, reveal some sensitivity to the Λ(1520) in-medium width. Therefore, their measurement in a dedicated experiment at the GSI pion beam facility will allow to shed light on this width.

Electron scattering from 1-butanol at intermediate impact energies: Total cross sections.

We report experimental measurements of the absolute total cross sections (TCSs) for electron scattering from 1-butanol at impact energies in the range 80-400 eV. Those measurements were conducted by considering the attenuation of a collimated electron beam, at a given energy, through a gas cell containing 1-butanol, at a given pressure, and through application of the Beer-Lambert law to derive the required TCS. We also report theoretical results using the Independent-Atom Model with Screening Corrected Additivity Rule and Interference approach. Those results include the TCS, the elastic integral cross section (ICS), the ionization total ICS, and the sum over all excitation process ICSs with agreement at the TCS level between our measured and calculated results being encouraging.

Absolute total ionization and dissociative ionization cross sections for H+ impact on N2O within the energy range of 2–10 keV

Measurements were made for the ionization and dissociative ionization of N2O in collisions with 2–10 keV protons. Absolute cross sections were obtained employing the time of flight mass spectroscopy for the slow target molecular ions and ionic fragments. Cross sections for the formation of single and doubly charged fragments are reported.

Absolute total cross sections for electron-impact double ionization of He(1s2s3S) and He−(1s2s2p4P)

We report on the experimental determination of absolute, total cross sections for electron-impact double ionization of helium in its metastable 1s 2s 3 S state and of the helium negative ion He− (1s 2s 2p 4 P). Cross sections are measured for impact energies ranging from threshold to 1000 eV using the animated crossed beams technique. The fast, pure beam of metastable helium required for the experiment is produced by photodetachment of fast He− ions. Results for He(1s 2s 3 S) are compared to those for He(1s 2 1 S), and exhibit similar magnitude and behaviour. The cross section for He− is large compared to other negative ions and indicates the predominance of indirect ionization channels at large impact energies.

Total cross-section for low-energy and very low-energy electron collisions with O2

An absolute total cross-section for electron scattering from O2 is obtained in the energy range from 20 eV down to 16 meV with a very narrow electron energy width of 7 meV, using the threshold-photoelectron source employing synchrotron radiation. The total cross-section obtained in the present study generally agrees well with those obtained in previous experimental works in the energy region where the previous experimental total cross-sections agree with each other. At lower energies, several features are found, including the very large contribution of the resonance to the total cross-section. The resonance energies and the resonance widths of the individual vibrational states of the resonance are determined from the analysis of the measured absolute total cross-section. The resonance width of the resonance of O2 is found to be much narrower than the value estimated from previous high-resolution experiments and theoretical calculations.

C-I and C-F bond-breaking dynamics in the dissociative electron ionization of CF3I.

We present a comprehensive experimental study into the dissociative electron ionization dynamics of CF3I at energies ranging from 20 to 100 eV. A beam-gas instrument has been used to measure the absolute total ionization cross-section for the molecule over the energy range from 0 to 300 eV. Coupled with data from an electron-molecule crossed beam velocity-map imaging instrument, this allows absolute partial ionization cross-sections to be determined for formation of each ionic fragment. These reveal a number of fragmentation channels involving both C-I and C-F bond cleavage, in some cases followed by further fragmentation of the resulting molecular ion. Velocity-map images have been recorded for the I+ and CF3+ products of C-I bond cleavage and the CF2I+ products of C-F bond cleavage. Analysis of fragment kinetic energy distributions extracted from the images reveals that CF3+ product of C-I bond cleavage appears to be formed via a statistical mechanism occurring over long timescales, while the CF2I+ products of C-F cleavage are formed via a much faster, more direct dissociation mechanism involving one or more repulsive states of the parent molecular ion. The I+ fragments arising from C-I bond cleavage display behaviour intermediate between the two extremes. For all fragments, the images show little or no dependence on the energy of the incident electron, implying that the initially excited ion state or states undergo rapid relaxation to the dissociative state(s) in all cases. Only a very small fraction of the incident electron's kinetic energy is released into kinetic energy of the recoiling atomic and molecular fragments, implying that most of the available energy remains with the two departing electrons. The kinetic energy distributions obtained for the various fragments of dissociative electron ionization are compared with the corresponding distributions reported from photoionization studies in order to gain insight into the electronic states involved.

Absolute total, partial, and differential cross sections for photodetachment of O−

Absolute total, partial, and differential cross sections for the photodetachment of the oxygen anion are reported for photon energies ranging from threshold (1.46 eV) to 5.5 eV. The total cross section was measured using the animated-crossed-beam technique while partial and differential cross sections were obtained using velocity map imaging. The measured values are in good agreement with theoretical results obtained from an $R$-matrix calculation using polarized pseudostates.

Mutual Neutralization of O^{-} with O^{+} and N^{+} at Subthermal Collision Energies.

We have measured total absolute cross sections for the mutual neutralization (MN) of O^{-} with O^{+} and N^{+}. A fine resolution (of about 50meV) in the kinetic energy spectra of the product neutral atoms allows unique identification of the atomic states participating in the mutual neutralization process. Cross sections and branching ratios have also been calculated down to 1meV center-of-mass collision energy for these two systems, with a multichannel Landau-Zener model and an asymptotic method for the ionic-covalent coupling matrix elements. The importance of two-electron processes in one-electron transfer is demonstrated by the dominant contribution of a core-excited configuration of the nitrogen atom in N^{+}+O^{-} collisions. This effect is partially accounted for by introducing configuration mixing in the evaluation of coupling matrix elements.

Total and Differential Cross-Sections of 16O(γ,n)3Heα8Be0 Reaction

The 16O(g,n)3He3a-reaction was investigated with the aid of the diffusion camera placed in the magnetic field and irradiated with a beam of bremsstrahlung g-quanta with an endpoint energy of 150 MeV. In to the curve of excitation of the system of 2a‑particles the resonance, identified as the ground state of the nucleus 8Be, were observed. The partial channels of production of these state (16O(g,n)3Hea8Ве0) were isolated and kinematical parameters of g-quantum and neutron were calculated. The absolute total cross-section of the partial channels in the energy interval from the threshold up to 120 MeV was measured. It has been established that the reaction is of a successive type: at first, the neutron is knocked out, and the residual nucleus 15О is in the excited state. The differential cross sections 16O(g,n)3Hea8Ве0-reaction has been measured and the dependence of the asymmetry coefficient distributions of the g-quantum energy and the excitation energy of the compound nucleus at the first intermediate stage of decomposition. The results are explained by the quantum interaction with a quasideuterons model.