Theory Of Electron-atom Collisions Research Articles

Calculation of Negative Ions and Scattering Using Methods of Electron Atom Collision Theory

Ab initio calculation of negative ions is made, and electron affinity energies, phase shifts and momentum transfer cross sections for electron-atom scattering are obtained using the techniques of many-body Green's functions. The basic processes treated here are the slow electron-alkaline earth atom scattering and the electron-noble gas atom scattering. Scattering data are obtained and negative ion calculations are made by solving the Dyson equation.

Born-Floquet theory of electron-atom collisions in the presence of a laser field

We present a theory of fast electron-atom collisions in the presence of a strong laser field, which treats the interaction of the laser field with both the projectile electron and the target atom in a fully non-perturbative way. The theory is illustrated by considering the laser-assisted ''elastic'' scattering of fast electrons by atomic hydrogen, for non-resonant as well as resonant cases.

Spin-resolved elastic scattering of electrons from sodium below the inelastic threshold.

A very stringent test of low-energy electron-atom collision theory is made in the most favorable energy regime for the close-coupling approximation. Data are presented as exchange asymmetries in angle-resolved elastic scattering of spin-polarized electrons from spin-polarized sodium atoms. Data are reported for two incident energies, 1.0 and 1.6 eV, both of which are below the first excited-state threshold. The angular range is 20--142.5\ifmmode^\circ\else\textdegree\fi{}. The close-coupling approximation is found to give excellent agreement with experiment at both energies.

On the use of the Bethe approximation in the treatment of long-range multipole interactions in electron-neutral-atom collisions

The integral IR(k, l, k', l', lambda )= integral ;r-( lambda +1)Fl(kr)Fl'(k'r)dr for dr R to infinity where Fl(kr)= square root k rjl(kr), jl is a spherical Bessel function and R>or=0, is considered and expressed in terms of well known functions. Its use in electron-atom collision theory is discussed. The interesting result of Burgess and Tully (1978) concerning the relationship of the weak-coupling Bethe and Born collision strengths in the limit of infinite impact energies, i.e. limE to infinity Omega Bethe I/ Omega Born I=2, is clarified.

Atomic data for opacity calculations. II. Computational methods

For pt.I see ibid., vol.20, p.6363-78 (1987). A general description of the data requirements for opacity calculations has been given in paper I. The present paper gives a detailed description of the methods being used in a collaborative effort which is referred to as the Opacity Project. The close-coupling approximation of electron-atom collision theory is used to calculate energies and wavefunctions for bound states, oscillator strengths, photoionisation cross sections and parameters for line broadening by electron impact. The computations are made using the R-matrix method together with new codes for calculating outer-region solutions and dipole integrals. Use of these techniques provides an efficient means of calculating large amounts of accurate atomic data.

Use of the R matrix method for bound-state calculations. I. General theory

In the close-coupling (CC) method of electron-atom collision theory, wavefunctions Psi E for a system containing (N+1) electrons are expanded in terms of products of N-electron 'target' functions multiplied by fully optimised orbital functions for a 'colliding' electron. The method can also be used to calculate energies En and functions Psi n for bound states of the (N+1)-electron system: this is often referred to as the 'frozen cores' (FCS) approximation. In the R-matrix method the CC problem is solved for an inner region, r or=a. The paper includes a discussion of the FCS approximation and a summary of R-matrix theory. Techniques are described for calculating orthonormal sets of outer-region solutions correct to first order in the long-range multipole potentials. Matching of inner-region to outer-region solutions gives an eigenvalue problem for the determination of the energies En which is solved using scanning techniques which do not require estimates of the En to be provided.

Impact, a program for the solution of the coupled integro-differential equations of electron-atom collision theory

Impact, a program for the solution of the coupled integro-differential equations of electron-atom collision theory

Impact, a program for the solution of the coupled integro-differential equations of electron-atom collision theory

Impact, a program for the solution of the coupled integro-differential equations of electron-atom collision theory

The strong-coupling method in the theory of electron-atom collisions

A review is presented of the present status of calculations, performed by the strong-coupling method, of the cross sections of electron-atom collisions. The main principles of the method are described, together with the procedures used for numerical calculations and with the properties of the results. The atoms for which calculations have been performed to date, and under what approximations, are reported and the published references are cited. The main problems arising in the calculations are discussed together with the methods used to resolve them. Proposed generalizations of the strong-coupling method are considered.

Metod sil'noi svyazi v teorii elektronno-atomnykh stolknovenii

Metod sil'noi svyazi v teorii elektronno-atomnykh stolknovenii

A method for calculating the algebra of matrix elements for photoionization and line radiation

This paper gives a detailed algebraic formulation of the matrix elements required in the calculation of photoionisation cross-sections and transition probabilities for line radiation. The formulation is based upon the Slater state expansion method: it is consistent with that developed by Eissner for calculating the angular coefficients required in setting up the coupled integro-differential equations of electron-atom collision theory. The formulation has been implemented in a general-purpose automatic computer program.

Eikonal theory of electron-atom collisions

The application of eikonal methods to electron-atom scattering is reviewed. After recalling the basic features of the eikonal approximation, we discuss the Glauber theory, the eikonal-Born series method, the eikonal optical model theory and the eikonal distorted wave approach. We also give a survey of recent results obtained for electron-hydrogen and electron-helium collisions at intermediate energies.

Asymptotic solutions of the coupled equations of electron-atom collision theory for the case of some channels closed

Solutions of coupled equations for electron-atom collision theory, having known asymptotic forms, can be calculated using asymptotic expansions at some large values of r, say r=rp and rp+1. At some smaller values of r, say r=r1 and r2, it is required to match the asymptotic solutions to solutions which are bounded at the origin. When some channels are closed, inwards integrations from (rp,rp+1) to (r1,r2) can give solutions which have poor linear independence at (r1,r2). It is shown that good linear independence can be obtained using a Fox-Goodwin technique for the solution of two-point boundary value problems.

On the validity of the distorted wave method in electron-atom collision theory

The comparison of distorted wave and close coupling calculations of collision strengths for transitions in C III excited by electron collisions indicates that the distorted wave method is sufficiently accurate for many astrophysical and laboratory applications even for atoms which are only twice ionized.

Electronic Spectroscopy by Electron Spectroscopy

Confronted with the stupefying flow of new information in the field of electronic spectroscopy, we have selected for review here three closely related topics likely to be less familiar to many of the readers of A nnual Reviews of Physical Chemistry than conventional spectroscopic methods. We do this in order to direct attention to a group of methods j ust now becoming especially fruitful for the study of electronic states of molecules. The methods are electron impact spectroscopy, photoelectron spectros­ copy, and Penning ionization spectroscopy. They have in common one facet that distinguishes them from conventional spectroscopy : all three of these methods use energy analysis of electrons, rather than energy analysis of photons, as the primary source of information. The three methods differ both in the manner by which excitation is induced, and in the kind of informa­ tion one obtains. I mpact spectroscopy obviously relies on transfer of kinetic energy from a free electron to the bound electrons of a target molecule or, as we shall often refer to it, a scatterer. This method is useful for studying normally empty levels, and particularly for studying transitions normally in conventional optical spectroscopy. Photoelectron spectros­ copy uses monoenergetic photons to remove bound electrons from targets and is particularly useful for studying normally occupied levels, including levels from the valence shells all the way to the most tightly bound K-shells. Penning spectroscopy is a new field, in which excitation is delivered to the target in the form of a quantum bound to an incoming atom, i.e., an excited, often metastable species. The Penning ionization process has the form A*+ M-7A+ M+ + e. This method is proving useful for the study of normally filled levels, particularly in the valence shell. Several reviews of topics related to electron spectroscopy should be noted. In connection with electron impact spectroscopy, the subject of forbidden transitions, the theory of excitation and ionization by electron impact and the measurement of these processes were reviewed in 1962 by Garstang (1) , Seaton (2) , and Fite (3) , respectively. Peterkop & Veldre have reviewed the theory of electron-atom collisions (4). Electron impact ionization cross sec­ tion data was surveyed by Kieffer & Dunn (5) , and Moiseiwitsch & Smith have reviewed electron impact excitation of atoms (6) . A review by Bardsley & Mandl of resonant electron-atom and electron-molecule collisions has

On the theory of electron-atom collisions

On the theory of electron-atom collisions

Electron exchange in binary encounter collision theory

The cross-section formulae for transfer of energy and momentum between a pair of free colliding electrons in an arbitrary frame in non-relativistic quantum mechanics have been derived. These formulae are applied in the electron-atom binary encounter collision theory in order to obtain the quantum-mechanical differential and total cross-section formulae for electron-atom collisions. This work represents an advance over the work of Gryzinski in that it includes interference between direct and exchange terms. Moreover, in the application some influence of the nucleus is taken into account since use is made of the symmetrical collision model. The interference term in the application to the binary encounter theory of electron-atom collisions corrects an earlier form of this term.

36. Theory of electron-atom collisions: G F Dhukarev,translated from the Russian by S Chanet, Academic Press, 1965

36. Theory of electron-atom collisions: G F Dhukarev,translated from the Russian by S Chanet, Academic Press, 1965