Table of contents

A specially designed magnetic spectrometer has been used in experiments to determine total e⁺-He scattering cross sections for positrons having energies between 50 and 400 eV. The results are in good agreement with calculated values but are larger than earlier experimental data.

The charge transfer cross section is independent of the ratio of the colliding masses. A proof is presented. It is further shown that this independence is implied in the formulation by Msezane and Gallaher (1974).

The angular distribution of O^- ions produced by the principal process for dissociative attachment of electrons in CO has been studied in the energy range from 9.8 eV to 11.2 eV for scattering angles from 10 to 120 degrees. The angular distribution is observed to have a strong asymmetry with respect to the 90 degree scattering angle as well as only a weak dependence on the incident energy. The observations indicate that only one resonant state is responsible for the attachment process, and a preliminary comparison with theory would suggest Pi symmetry for the intermediate negative ion state.

Alkali-like atoms are treated from the viewpoint of broken O₄-symmetry. The outer electron is described by a single-particle Hamiltonian operator which is the sum of a hydrogenic Hamiltonian and a symmetry-breaking operator V. The O₄-transformation properties of V are studied by expanding V in a series of O₄-tensor operators T( Gamma ). This evaluation is accomplished by a comparison with experimental energy levels through a Z^-1 expansion for the Li I and Na I isoelectronic sequences.

The polarization propagator is analysed in the random phase approximation for atoms with two electrons in an open shell and a core of completely filled shells. The connection between optimization of the energy and the requirement that the so-called B and C matrices should be Hermitian is discussed. Particle-hole symmetry in RPA for open shell systems is examined, and it is shown how RPA formulae for the configurations (nl)¹, (nl) ^4l+1, and (nl)^4l+2 can be derived from the results for (nl)². The calculation of oscillator strengths from the residues of the propagator is described. Numerical results for silicon I are presented. Finally the applicability of the method is discussed.

For pt.I see abstr. A5739 of 1975. Frozen core Hartree-Fock wavefunctions were used in an ab initio configuration-interaction calculation which included the effects of the spin-orbit interaction. A total of 160 allowed transition probabilities between 28 J=1, excited states of Ne I along with the associated eigenvalues were produced. The configurations involved are 2p⁵ns, n=3 to 6; 2p⁵np, n=3,4; and 2p⁵nd, n=3 to 6. Previous data, experimental or theoretical, exists for only 72 of the transitions studied.

The atomic spectrum of oxygen has been excited in an electrodeless discharge lamp; depending on the wavelength the lines have been analysed by means of Fabry-Perot or Fourier spectrometry. The fine structure of the 2p³(⁴S)3d ^3,5D terms have been re-measured with an uncertainty of about 0.2 mK; those of the terms 2p³(⁴S)4d ^3,5D have been resolved and determined with an uncertainty less than 2 mK. The fine structure intervals of the quintet terms are found to obey the Casimir formula within the limits of the experimental errors; for each triplet and each quintet the radial quantities A' and B' involved in this formula are obtained. In order to interpret theoretically the values of these constants, the Breit-Dirac equation and the equivalent operators formalism are used. In a pure coupling scheme, ab initio calculations of the various magnetic interactions (spin-orbit, spin-other-orbit, spin-spin interactions) do not give satisfactory results but, by taking into account higher-order terms, a good agreement between experimental and theoretical (ab initio) values is achieved.

Various electronic correlation effects associated with the photoionization of alkalis are examined in detail by the use of many-body perturbation theory. With the inclusion of all important correlation effects, in particular, the effect of virtual excitation of inner shell electrons, the author removed most of the existing discrepancies between experimental observations and theoretical calculation.

For pt.I see ibid., vol.7, p.2495 (1974). The two-potential calculation for the S-wave phase shift is generalized by replacing the square well potential with a series of square well potential steps for r<or=R such that the residual potential now becomes negligibly weak. Therefore, the values of tan delta _l (l>or=0) and the scattering amplitude f( theta ) for the exponential and screened Coulomb potentials as well as for the scattering of electrons by the static potential of atomic hydrogen. The results obtained agree well with those given by the Fredholm integral equation method and the Runge-Kutta method.

For pt.I see abstr. A12506 of 1974. The author's previously reported calculations on electron impact excitation of hydrogenic ions are extended by the inclusion of magnetic effects and retardation into the interaction between the two electrons, both the Breit and the Moller interactions being used. These effects are found to contribute 4% or less to the cross sections for Z=25 but become much larger for increasing atomic number. The effect of an improved approximation for the screening of the nucleus by the bound electron (distorted wave instead of Coulomb-Born) is also investigated and found to be small.

Ionization cross sections of Li⁺, B³⁺, O⁶⁺, Ne⁸⁺ and Mg¹⁰⁺ by electron impact have been calculated semiempirically from threshold to 30 keV. The results are in reasonably good agreement with the available experimental and theoretical data.

Collision strengths are given for inner-shell excitation by electron impact of the levels of the 1s2s², 1s2s2p and 1s2p² configurations of highly charged lithium-like ions.

Valence Compton profiles and momentum expectation values for some small and medium-sized molecules are calculated and analysed using Fourier transformed wavefunctions obtained by means of the semi-empirical (iterative) extended Huckel, CNDO/2 and INDO methods. Particular attention is paid to the alleged insensitivity of the molecular profile, and the question of bond profile transferability is briefly discussed in an INDO localized picture.

The fine structure of the ⁷ Pi and ⁷ Sigma electronic states of MnH have been investigated. The molecular Hamiltonian including centrifugal distortion effects has been discussed using case a wavefunctions with definite parity as basis set. An iteration procedure based on numerical matrix diagonalization combined with a least square fit takes the interactions between the ⁷ Pi and ⁷ Sigma states into account and calculates upper and lower state molecular constants simultaneously. The unusually large Lambda -type doubling of the ⁷ Pi state could also be well interpreted within the framework of this model.

A tandem mass spectrometer has been used to measure the distribution of ionic products resulting from the reaction of D₃⁺ with CH₄ as a function of the average number of D₃⁺-D₂ collisions occurring in the source. These results provide information on the amount of internal excitation energy in D₃⁺. It is shown that at least 69% of the D₃⁺ ions are formed with 0.6 eV or more excitation energy. These results are compared with an approximate D₃⁺ excitation energy distribution based upon a statistical model which assumes a random distribution of energy among the vibrational and translational states of the products of the reaction of D₂⁺ with D₂. Reasonable agreement was obtained.