Information on the spectrum of oscillator strength for neutral atoms in their ground states is surveyed with particular regard to recent progress in the far uv-soft x-ray range and to the theoretical interpretation of data from experiments and from numerical calculations. The analysis brings out numerous aspects of atomic mechanics and problems that remain unsolved. An effort is made to interconnect different theoretical approaches within the framework of the theory of atomic spectra.

Spectral Distribution of Atomic Oscillator Strengths

I. Introduction and Scope 231A. Definitions of Atomic Electron Affinities 233B. Definitions of Molecular Electron Affinities 233II. Experimental Photoelectron Electron Affinities 235A. Historical Background 235B. The Photoeffect 236C. Experimental Methods 237D. Time-of-Flight Negative Ion PhotoelectronSpectroscopy239E. Some Thermochemical Uses of ElectronAffinities241F. Layout of Table 10: ExperimentalPhotoelectron Electron Affinities242III. Theoretical Determination of Electron Affinities 242A. Historical Background 2421. Theoretical Predictions of Atomic ElectronAffinities2422. Theoretical Predictions of MolecularElectron Affinities243B. Present Status of Theoretical Electron AffinityPredictions243C. Basis Sets and Theoretical Electron Affinities 244D. Density Functional Theory (DFT) andElectron Affinities245E. Layout of Tables 8 and 9: Theoretical DFTElectron Affinities247F. Details of Density Functional MethodsEmployed in Tables 8 and 9247IV. Discussion and Observations 248A. Statistical Analysis of DFT Results ThroughComparisons to Experiment and OtherTheoretical Methods248B. Theoretical EAs for Species with UnknownExperimental EAs251C. On the Applicability of DFT to Anions and theFuture of DFT EA Predictions251D. Specific Theoretical Successes 251E. Interesting Problems 2521. C

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Atomic and molecular electron affinities: photoelectron experiments and theoretical computations.

In this review we present the energies, configuration, and other properties of resonances (also called "compound states" and "temporary negative ions") in diatomic molecules. Much of the information is presented in the form of tables and energy level diagrams. Vibrational, rotational, and electronic excitation are discussed whenever these processes have given information on resonances; often these excitation processes proceed via resonances. The paper is divided according to molecular species (${\mathrm{H}}_{2}$, ${\mathrm{N}}_{2}$, CO, NO, ${\mathrm{O}}_{2}$), but the main conclusions are discussed by the nature of the processes involved.

Resonances in Electron Impact on Diatomic Molecules

Angular Distribution of Photoelectrons

We show how the presence of a conical intersection in the adiabatic potential energy hypersurface can be handled by including a new vector potential in the nuclear‐motion Schrodinger equation. We show how permutational symmetry of the total wave function with respect to interchange of nuclei can be enforced in the Born–Oppenheimer approximation both in the absence and the presence of conical intersections. The treatment of nuclear‐motion wave functions in the presence of conical intersections and the treatment of nuclear‐interchange symmetry in general both require careful consideration of the phases of the electronic and nuclear‐motion wave functions, and this is discussed in detail.

On the determination of Born–Oppenheimer nuclear motion wave functions including complications due to conical intersections and identical nuclei

Atomic Collision Processes

Experiments and theory on the continuous absorption of radiation by atomic-oxygen negative ions are described and discussed. The absorption cross section for photon energies not too near threshold is obtained directly from one of the experiments. Theory and experiment are combined to give the cross section in the vicinity of threshold and a precise value of the electron affinity of atomic oxygen. The latter result is EA(O) = 1.465\ifmmode\pm\else\textpm\fi{}0.005 ev. The data are used for computation of the radiative attachment coefficient, and other applications of the experimental results are discussed.

Photodetachment Cross Section and the Electron Affinity of Atomic Oxygen

The recent measurement of the transition probability for the double-quantum detachment of an electron from ${\mathrm{I}}^{\ensuremath{-}}$ has prompted a new theoretical study of this problem. A central-field model for bound and free states is used, in which a parameter is adjusted in the potential to yield the observed binding energies of the negative ions. An implicit-sum method, requiring the solution of inhomogeneous radial equations, is used to evaluate the sums over intermediate states. The results for ${\mathrm{I}}^{\ensuremath{-}}$ lie almost within the experimental uncertainty. The cross sections for single-quantum photodetachment and electron elastic scattering (from the neutral atom) are also given for the ions studied: ${\mathrm{C}}^{\ensuremath{-}}$, ${\mathrm{O}}^{\ensuremath{-}}$, ${\mathrm{F}}^{\ensuremath{-}}$, ${\mathrm{Si}}^{\ensuremath{-}}$, ${\mathrm{S}}^{\ensuremath{-}}$, ${\mathrm{Cl}}^{\ensuremath{-}}$, ${\mathrm{Br}}^{\ensuremath{-}}$, ${\mathrm{I}}^{\ensuremath{-}}$.

Single- and Double-Quantum Photodetachment of Negative Ions

Topics in Atomic Collision Theory

The energies of the lowest He-like compound-atom or resonance states lying below the $n=2$ hydrogenic level are evaluated variationally for He and ${\mathrm{H}}^{\ensuremath{-}}$. In order to do this, we employ the definition of such states given by Feshbach as eigenvalues of the Hamiltonian with the open channel projected out, together with the modification required by the Pauli principle. Our trial wave function uses a Legendre expansion in the relative angle and a sum of exponentials in the radial coordinates, with appropriate angular factors to obtain the desired symmetry, parity, and orbital-angular-momentum eigenvalues associated with the $^{1,3}S^{e}$ and $^{1,3}P^{o}$ states. Our results are approximations to the actual physical resonances in that the shift and finite width caused by coupling to the neighboring continuum are not included. It appears, however, that the actual shifts are small, so that the positions of these compound-atom states are believed to give a close indication of where the physical resonances may be expected to occur. The results for He and ${\mathrm{H}}^{\ensuremath{-}}$ are compared in detail with the calculations of resonances in $e$-H and $e$-${\mathrm{He}}^{+}$ elastic scattering and with the observation of these states by ultraviolet photon absorption in He (where they are called autoionizing levels) and by inelastic scattering of electrons from He.

Sydney Geltman

Papers

Atomic Collision Processes

Photodetachment Cross Section and the Electron Affinity of Atomic Oxygen

Single- and Double-Quantum Photodetachment of Negative Ions

Topics in Atomic Collision Theory

Compound-Atom States for Two-Electron Systems