A Novel Approach to Measuring Inelastic Differential Cross Sections for Electron-Molecule
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Electron-Molecule Collisions↗
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A Novel Approach to Measuring Inelastic Differential Cross Sections for Electron-Molecule
Explore the source record for details and available documents.
Electron-Molecule Collisions↗
Recent measurements concerning uranium hexafluoride-electron collision processes
Scattering of electrons by UF6 molecules was studied at impact energies ranging from 5 to 100 eV and momentum transfer, elastic and inelastic scattering cross sections were determined. The measurements also yielded spectroscopic information which made possible to extend the optical absorption cross sections from 2000 angstroms to 435 angstroms. It was found that UF6 is a very strong absorber in the vacuum UV region. No transitions were found to lie below the onset of the optically detected 3.0 eV feature.
Trajmar, S.↗
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↗
Rotational and vibrational transitions for Li + H2 collisions
Close coupling calculations for integral and differential cross sections have been carried out for Li + H2 collisions with an ab initio Hartree-Fock potential energy surface. Rotational, vibrational, and vib-rotational excitation cross sections are reported at 0.4336 eV, 0.7 eV, and 0.8673 eV in the center of mass system. For pure rotational excitations, which dominate the inelastic scattering, coupling with vibrational states is not very important. For vibrational transitions, the influence of large multiquantum rotational transitions is far less than that found for Li(+) + H2 collisions.
Choi, B. H.↗
Microgravity Segregation in Binary Mixtures of Inelastic Spheres Driven by Velocity Fluctuation Gradients
We are interested in collisional granular flows of dry materials in reduced gravity. Because the particles interact through collisions, the energy of the particle velocity fluctuations plays an important role in the physics. Here we focus on the separation of grains by properties - size, for example - that is driven by spatial gradients in the fluctuation energy of the grains. The segregation of grains by size is commonly observed in geophysical flows and industrial processes. Segregation of flowing grains can also take place based on other properties, e.g. shape, mass, friction, and coefficient of restitution. Many mechanisms may be responsible for segregation; most of these are strongly influenced by gravity. Here, we outline a mechanism that is independent of gravity. This mechanism may be important but is often obscured in terrestrial grain flows. It is driven by gradients in fluctuation energy. In microgravity, the separation of grains by property will proceed slowly enough to permit flight observations to provide an unambiguous measurement of the transport coefficients associated with the segregation. In this context, we are planning a microgravity shear cell experiment that contains a mixture of two types of spherical grains. The grains will be driven to interact with two different types of boundaries on either sides of the cell. The resulting separation will be observed visually.
Jenkins, James T.↗
Theoretical line shapes for rotational spectra of HCl in Ar
An interaction potential for HCl-Ar recently derived from spectra of van der Waals complexes (Hutson,1988) has been used to obtain converged close-coupling scattering S matrices from which pressure broadening (linewidth, line shift, and line coupling) cross sections have been computed within the Fano-Ben-Reuven formalism. Linewidths agree well with experimental data with the exception of the 0-1 line at low temperatures (an error of about 15 percent at 125 K). Line shifts, especially the largest, for the 0-1 line, are also in reasonable accord with experimental data. Line coupling is predicted to be quite small. The coupled-states molecular scattering approximation is found to be accurate except at very low collision energies. The infinite-order sudden approximations, on the other hand, is not reliable for this system. Inelastic scattering out of the spectroscopic levels accounts for only a fraction of the linewidth at thermal energies, especially in the lower rotational levels.
Green, Sheldon↗
Molecular collisions. XVI.
The comparison indicates that the present version of the GPS method overestimates the rotational excitation and underestimates the de-excitation, while maintaining the total inelasticity at approximately the correct exact classical trajectory value. An approximate ?quantization' of the classical results leads to an estimate of the quantal cross sections corresponding to changes by plus or minus 2, 4, and 6 from an initial rotor quantum state 10. It is found that most of the total inelastic cross section arises from the first-order-allowed transitions.
Pattengill, M. D.↗
Experimental and data analysis techniques for deducing collision-induced forces from photographic histories of engine rotor fragment impact/interaction with a containment ring
An analysis method termed TEJ-JET is described whereby measured transient elastic and inelastic deformations of an engine-rotor fragment-impacted structural ring are analyzed to deduce the transient external forces experienced by that ring as a result of fragment impact and interaction with the ring. Although the theoretical feasibility of the TEJ-JET concept was established, its practical feasibility when utilizing experimental measurements of limited precision and accuracy remains to be established. The experimental equipment and the techniques (high-speed motion photography) employed to measure the transient deformations of fragment-impacted rings are described. Sources of error and data uncertainties are identified. Techniques employed to reduce data reading uncertainties and to correct the data for optical-distortion effects are discussed. These procedures, including spatial smoothing of the deformed ring shape by Fourier series and timewise smoothing by Gram polynomials, are applied illustratively to recent measurements involving the impact of a single T58 turbine rotor blade against an aluminum containment ring. Plausible predictions of the fragment-ring impact/interaction forces are obtained by one branch of this TEJ-JET method; however, a second branch of this method, which provides an independent estimate of these forces, remains to be evaluated.
Yeghiayan, R. P.↗
The Schwinger Variational Method
Variational methods have proven invaluable in theoretical physics and chemistry, both for bound state problems and for the study of collision phenomena. The application of the Schwinger variational (SV) method to e-molecule collisions and molecular photoionization has been reviewed previously. The present chapter discusses the implementation of the SV method as applied to e-molecule collisions. Since this is not a review of cross section data, cross sections are presented only to server as illustrative examples. In the SV method, the correct boundary condition is automatically incorporated through the use of Green's function. Thus SV calculations can employ basis functions with arbitrary boundary conditions. The iterative Schwinger method has been used extensively to study molecular photoionization. For e-molecule collisions, it is used at the static exchange level to study elastic scattering and coupled with the distorted wave approximation to study electronically inelastic scattering.
Huo, Winifred M.↗
Ab initio Potential-Energy Surfaces and Electron-Spin-Exchange Cross Sections for H-O2 Interactions
Accurate quartet- and doublet-state potential-energy surfaces for the interaction of a hydrogen atom and an oxygen molecule in their ground states have been determined from an ab initio calculation using large-basis sets and the internally contracted multireference configuration interaction method. These potential surfaces have been used to calculate the H-O2 electron-spin-exchange cross section; the square root of the cross section (in a(sub 0)), not taking into account inelastic effects, can be obtained approximately from the expressions 2.390E(sup -1/6) and 5.266-0.708 log10(E) at low and high collision energies E (in E(sub h)), respectively. These functional forms, as well as the oscillatory structure of the cross section found at high energies, are expected from the nature of the interaction energy. The mean cross section (the cross section averaged over a Maxwellian velocity distribution) agrees reasonably well with the results of measurements.
Stallcop, James R.↗
Molecular collisions. IX - Restricted distorted-wave approximation for rotational excitation and scattering of diatomic molecules.
Rotational excitation and scattering cross sections for rigid diatomic molecules reduced to yield distorted wave approximation, resulting in inelastic transition probabilities
Bernstein, R. B.↗
Reaction and electronic excitation in crossed-beams collisions of low-energy O(3P) atoms with H2O and CO2
Collisions of low-energy (5-20 eV), ground-state oxygen atoms with H2O and CO2 in a crossed-beams geometry lead to chemical reaction in the case of H2O to produce OH (A2Sigma+ - X2Pi) emissions; and to inelastic electronic excitation in the case of CO2 to produce CO2 flame bands. Species identifications are made through known wavelengths and emission intensities in the range 300-400 nm. The measured difference in threshold energies for the two processes confirm the channels involved. These are the first measurements in this energy range of optical emissions through collisions of fast neutral species.
Orient, O. J.↗
The role of orbital dynamics and cloud-cloud collisions in the formation of giant molecular clouds in global spiral structures
The role of orbit crowding and cloud-cloud collisions in the formation of GMCs and their organization in global spiral structure is investigated. Both N-body simulations of the cloud system and a detailed analysis of individual particle orbits are used to develop a conceptual understanding of how individual clouds participate in the collective density response. Detailed comparisons are made between a representative cloud-particle simulation in which the cloud particles collide inelastically with one another and give birth to and subsequently interact with young star associations and stripped down simulations in which the cloud particles are allowed to follow ballistic orbits in the absence of cloud-cloud collisions or any star formation processes. Orbit crowding is then related to the behavior of individual particle trajectories in the galactic potential field. The conceptual picture of how GMCs are formed in the clumpy ISMs of spiral galaxies is formulated, and the results are compared in detail with those published by other authors.
Roberts, William W., Jr.↗
A time-dependent wave packet approach to atom-diatom reactive collision probabilities - Theory and application to the H + H2(J = 0) system
This paper describes a new approach to the study of atom-diatom reactive collisions in three dimensions employing wave packets and the time-dependent Schroedinger equation. The method uses a projection operator approach to couple the inelastic and reactive portions of the total wave function and optical potentials to circumvent the necessity of using product arrangement coordinates. Reactive transition probabilities are calculated from the state resolved flux of the wave packet as it leaves the interaction region in the direction of the reactive arrangement channel. The present approach is used to obtain such vibrationally resolved probabilities for the three-dimensional H + H2 (J = 0) hydrogen exchange reaction, using a body-fixed system of coordinates.
Neuhauser, Daniel↗
Comment on the accuracy of Rabitz' effective potential approximation for rotational excitation by collisions
Cross sections for rotational excitation of HCN by low-energy collisions with He have been computed with the effective-potential approximation of Rabitz (1972) and compared with accurate quantum close-coupling results. Elastic cross sections are found to agree to about 20%; inelastic cross sections agree in general magnitude, but not in detailed values for specific quantum transitions.
Green, S.↗
Production of H-3 at large momentum in alpha-(C-12) collisions at 2A GeV
Calculations of the longitudinal and transverse momentum distributions for H-3 production at large momentum in alpha-(C-12) collisions near 2A GeV are compared to experiment. Triton exchange and final-state interactions are shown to represent large corrections to the impulse approximation for proton knockout. A method for calculating interference effects for inelastic fragmentation is discussed. Good agreement with experiment using a phenomenological overlap function for (H-3)-p is found successful in describing H-3 production in pion-induced reactions. Comparisons to momentum distributions obtained through (p, 2p) and (e, ep) reactions on He-4 are made.
Cucinotta, Francis A.↗
Molecular beams in chemistry.
The molecular-beam technique is a means for producing isolated atoms or molecules within a narrow range of speed and solid angle. The phenomena studied with molecular beams can be classified as single-particle interactions, many-particle interactions, and two particle-interactions. The results of scattering experiments fall into two categories including collisions that do not result in atomic rearrangements and collisions that do. Experimental methods are discussed, giving attention to low-energy beams, high-energy beams, and intermediate-energy beams. Examples are presented to illustrate the information that can be obtained from elastic, inelastic, and reactive scattering.
Jordan, J. E.↗