Interaction of 42 MeV alpha-particles with He3
Differential elastic cross sections of 42 MeV alpha particles scattering from He 3, using optical model with spin-orbit potential
Boschitz, E. T.↗
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A comparison of DWBA and coupled channels in the 2s-1d shell
DWBA optical model coupled channels comparison in 2s-1d shell for predicting proton scattering elastic cross sections
Ascuitto, R. J.↗
Internuclear dependence of the polarizability of N2
A study is made of the internuclear dependence of the polarizability of N2. Specifically, the dependencies of parallel and perpendicular polarizabilities on internuclear separation is found for the N2 molecule in its ground state. Results are presented for vibrationally elastic cross sections as functions of incident electron energy in an eight-state calculation and for the excitation of the first vibrational state.
Temkin, A.↗
Inclusion of electron correlation for the target wave function in low- to intermediate-energy e-N2 scattering
In a recent calculation, an exact exchange method was developed for use in the partial-differential-equation approach to electron-molecule scattering and was applied to e-N2 scattering in the fixed-nuclei approximation with an adiabatic polarization potential at low energies (0-10 eV). Integrated elastic cross sections were calculated and found to be lower than experiment at energies both below and above the Pi(g) resonance. It was speculated at that time that improved experimental agreement could be obtained if a correlated target representation were used in place of the uncorrelated one. The present paper implements this suggestion and demonstrates the improved agreement. These calculations are also extended to higher energies (0-30 eV) so asd to include the Sigma(u) resonance. Some discrepancies among the experiments and between experiment and the various calculations at very low energy are noted.
Weatherford, C. A.↗
Ab initio R-matrix calculations of e+-molecule scattering
The adaptation of the molecular R-matrix method, originally developed for electron-molecule collision studies, to positron scattering is discussed. Ab initio R-matrix calculations are presented for collisions of low energy positrons with a number of diatomic systems including H2, HF and N2. Differential elastic cross sections for positron-H2 show a minimum at about 45 deg for collision energies between 0.3 and 0.5 Ryd. The calculations predict a bound state of positronHF. Calculations on inelastic processes in N2 and O2 are also discussed.
Danby, Grahame↗
Electron-impact excitation cross sections for the b 3Sigma(+)nu state of H2
Differential and integral cross sections for electron-impact excitation of the b 3Sigma(+)nu state of H2 have been determined in the 20-100-eV impact energy region. The calibration of the cross sections was achieved through the H2 elastic scattering cross sections, which in turn were normalized to absolute He elastic scattering cross sections. Comparison is made with available experimental data and with theoretical results applying Born-Ochkur-Rudge, distorted-wave, and close-coupling approximations.
Khakoo, M. A.↗
Cross Sections, relic abundance, and detection rates for neutralino dark matter
Neutralino annihilation and elastic scattering cross sections are derived which differ in important ways from previous work. These are applied to relic abundance calculations and to direct detection of neutralino dark matter from the galactic halo. Assuming the neutralino to be the lightest supersymmetric particle and that it is less massive than the Z sup 0, we find relic densities of neutralinos greater than 4 percent of critical density for almost all values of the supersymmetric parameters. We constrain the parameter space by using results from PETRA (chargino mass less than 23 GeV) and ASP, and then assuming a critical density of neutralinos, display event rates in a cryogenic detector for a variety of models. A new term implies spin independent elastic scattering even for those majorana particles and inclusion of propagator momenta increases detection rates by 10 to 300 percent for pure photinos. Z sup 0-squark interference leads to very low detection rates for some values of the parameters. The new term in the elastic cross section dominates for heavy, mostly spinless materials and mitigates the negative interference cancellations in light materials; except for the pure photino or pure higgsinos cases where it does not contribute. In general, the rates can be substantially different from the pure photino and pure higgsino special cases usually considered.
Griest, Kim↗
Electron detachment from negative ions - The effects of isotopic substitution
Absolute total electron-detachment cross sections and relative elastic-scattering cross sections are presented for collisions of H(-) or D(-) with He, Ne, Ar, and N2 for collision energies ranging from about 2 eV up to 100 eV. Special emphasis has been given to the effect of isotopic substitution. It was found that, with the exception of the helium target, the results cannot be in accord with a model using a localized complex potential. On the other hand, the results for H(-) or D(-) with He are in excellent agreement with predictions based on previous (local complex potential) analysis of differential elastic-scattering measurements.
Champion, R. L.↗
Ionospheric dynamo theory for production of far ultraviolet emissions on Uranus
A model is presented to explain diffuse FUV emissions from the outer planets, specifically Uranus, in excess of those diffuse emissions that are currently explainable by scattering of sunlight and/or excitation by photoelectrons. These electroglow emissions in H Ly-alpha and H2 bands, which occur in the sunlit hemisphere slightly above the homopause, appear to require particle excitation in the 10- to 50-eV range. An in situ mechanism for accelerating photoelectrons (and ions is proposed, involving neutral wind dynamo generation of field-aligned currents analogous to what occurs in the earth's equatorial E and F regions. Sufficiently strong field-aligned currents are found in the model calculation for Uranus to produce a potential drop of about 100 eV or greater between the F peak and homopause, concentrated at lower altitudes, and capable in principle of accelerating photoelectrons (and ions) to the 10- to 50-eV energies required to explain the observed emissions. The fact that the excitation and ionization cross sections are larger than elastic scattering cross sections in an H2 atmosphere at these energies makes in situ acceleration feasible for the production of UV on the outer planets.
Hudson, M. K.↗
Low-energy electron-atom bremsstrahlung
This paper extends recent work providing an elementary calculation of bremsstrahlung and opacity associated with the scattering of low-energy electrons by neutral atoms and molecules. The method applies when the scattering potential is 'hard' or when the collision time is short, applying the classical soft-photon emission probability formula for arbitrary bremsstrahlung photon energy. However, now, in addition to correcting the probability factor for finite bremsstrahlung photon energy, another factor corrects for the reduced phase space available to the outgoing electron. The bremsstrahlung cross section and opacity are then computed directly from the elastic scattering cross section, determined experimentally or calculated; a small (approximately 10 percent) correction is computed from the anisotropic term in the elastic scattering cross section. The opacity is evaluated for electron scattering by H, He, and H2 using experimentally determined values for the elastic scattering cross section, and is compared with more elaborate calculations. The agreement is good (within 10 percent), indicating an accuracy for the general method comparable to variations among the results of different elaborate theoretical computations. The agreement seems to validate the basic approximation of short collision time even at large bremsstrahlung photon energy for electron energies and temperatures up to a few eV.
Gould, R. J.↗
The Extrema-effect in Total Elastic Molecular Beam Scattering Cross Sections for Characterization of the Potential Well
Extrema effect in total elastic molecular beam scattering cross sections for characterization of potential well
POTENTIAL ENERGY↗
Extrema-effect in total elastic molecular beam scattering cross sections for characterization of the potential well.
Extrema-effect in total elastic molecular beam scattering cross sections for characterizing potential well
MOLECULAR COLLISION↗
Elastic scattering of electrons from SO2
A crossed electron beam-molecular beam scattering geometry and the relative-flow technique are used to measure the ratios of the elastic differential cross sections of SO2 to those of He at electron impact energies of 12, 20, 50, 100, 150, and 200 eV. At each energy, an angular range of 15-150 deg is covered. The ratios are multiplied by previously known He elastic differential cross sections to obtain elastic differential cross sections for SO2. Integral and momentum transfer cross sections are then determined from a knowledge of differential cross sections. With the aid of the two-potential theory of e-molecule scattering, calculations are also performed and compared with the measurements.
Orient, O. J.↗
Absolute elastic differential electron scattering cross sections in the intermediate energy region. III - SF6 and UF6
A recently developed technique has been used to measure the ratios of elastic differential electron scattering cross sections (DCS) for SF6 and UF6 to those of He at electron impact energies of 5, 10, 15, 20, 30, 40, 50, 60, and 75 eV and at scattering angles of 20 to 135 deg. In order to obtain the absolute values of DCS from these ratios, He DCS of McConkey and Preston have been employed in the 20 to 90 deg range. At angles in the 90 to 135 deg range the recently determined cross sections of Srivastava and Trajmar have been utilized. From these DCS, elastic integral and momentum transfer cross sections have been obtained.
Srivastava, S. K.↗
Electron-impact excitation of the low-lying electronic states of HCN
The first study of the low-energy electron-impact excitation of low-lying electronic transitions in the HCN molecule is reported. Measurements were made at incident electron energies of 11.6 and 21.6 eV in the energy-loss range of 3-10 eV, and at scattering angles of 20-130 deg. Inelastic scattering spectra were placed on the absolute cross-section scale by determining first the ratio of inelastic-to-elastic scattering cross sections, and then separately measuring the absolute elastic scattering cross section. Several new electronic transitions are observed which are intrinsically overlapped in the molecule itself. Assignments of these electronic transitions are suggested. These assignments are based on present spectroscopic and cross-sections measurements, high-energy electron scattering spectra, optical absorption spectra, and ab initio molecular orbital calculations.
Chutjian, A.↗
Determination of differential elastic and vibrational excitation cross sections for e-H sub 2 scattering
Elastic scattering of electrons by hydrogen
Brinkmann, R. T.↗
Principles and procedures for determining absolute differential electron-molecule (atom) scattering cross sections
Procedures and calibration techniques for measuring the absolute elastic and inelastic differential cross sections (DCS) for electron impact on molecular (atomic) species are described and illustrated by examples. The elastic DCS for the molecule under study is first determined by calibration against helium using the relative flow technique. The second step involves the production of energy-loss spectra for the instrument response function, the unfolding of overlapping inelastic structures and the normalization of inelastic intensities to the elastic cross sections. It is concluded that this method of determining absolute differential electron-molecule (atom) scattering cross sections is generally applicable and provides reliable results.
Nickel, J. C.↗
Bremsstrahlung in the scattering of low-energy electrons by neutral atomic systems
By elementary methods, the cross section for electron-atom and electron-molecule bremsstrahlung is computed in the limit when the incident electron energy is much less than Ry. The procedure employs the classical soft-photon emission probability formula for general (h/2pi)(omega), yielding a simple expression for the bremsstrahlung cross section in terms of the total elastic scattering cross section. The validity of the method is discussed, and results are compared with more elaborate and accurate calculations. Comparison is made with ('free-free') opacity calculations for the associated process at the temperature (6300 K) of the solar atmosphere. For chi sub omega = (h/2pi)(omega)/kT = 1, the computed absorption coefficient is within 2, 7, and 12 percent of accurate calculations for scatterings by H, He, and H2, respectively. The general dependence of the opacity on chi sub omega is described well by the simple formula, although the error is larger for higher chi sub omega; it is suggested that the inaccuracy at high frequencies is due to the failure of the soft-photon approximation.
Gould, R. J.↗