Table of contents

It is shown that a process for producing totally polarized electrons proposed by Fargo and Walker (1973) can also be obtained as a special case in three-photon ionization of an alkali atom. No dependence of the radial matrix elements on the total angular momentum is necessary, nor is it assumed.

Collision strengths for N⁺ 2s²2p²³P-¹D and ³P-¹S have been calculated allowing for configuration interaction between 2s²2p² and 2p⁴ and with inclusion of 2s2p³ states in the close coupling expansion. Use of the same approximations for the calculation of bound states in neutral N indicates that the collision strengths should be correct to within about 10%. Inclusion of the 2s2p³ states does not give a large change in the near-threshold collision strengths; this result is in disagreement with that obtained by Ormonde et al (1971) and Ormonde et al (1973).

It is suggested that diatomic antibonding sigma *s molecular orbitals rather than p atomic orbitals, can function as the 'metallic orbitals' in the simplest account of the Pauling valence-bond theory of electron conduction in alkali metals.

The broadening and the shift of the Na D₁ and D₂ lines perturbed by atomic hydrogen are calculated taking into account accurate molecular potentials and non-adiabatic and fine structure effects. It is shown that the contribution of the ground state to the perturbed profile is predominant. The two components are broadened almost in the same manner whereas the shifts exhibit a difference of 20% at 4500K. The results obtained fit well with the observed wings of the absorption line profiles under the conditions of the solar photosphere. Cross sections for transitions induced between the fine structure states are calculated with and without taking into account the rotation of the internuclear axis. Non-adiabatic effects are shown to be of the order of 20%.

Non-relativistic potentials, mass polarization corrections and relativistic contributions of order alpha ² ry are obtained theoretically for the n^1,3S and the n^1,3P(n<or=5) states of all two-electron ions with Z in the range 11<or=Z<or=42. Radiative (QED) corrections of order alpha ³ ry are estimated for the ground and n^1,3S, n^1,3P(n=2,3) states throughout the range 4<or=Z<or=42. Estimates for the singlet-triplet corrections to the n^1,3P₁ potentials (n<or=5) and of the corresponding singlet-triplet mixing coefficients were made in the range 3<or=Z<or=42. For completeness, all these quantities have been tabulated over the entire range 2<or=Z<or=42. In addition the fine structure intervals and interval ratios in the n³P states have been tabulated in this range. The accuracies of the ionization potentials and all the various corrections are specified. Some applications of the results are discussed.

The satellite band on the red wing of the potassium line at lambda 4047 Å pressure broadened by krypton has been observed at temperatures of 900K, 650K and 250K. As the temperature is reduced the shape of the band becomes sharper as is predicted by the theory of red satellite bands advanced by Hindmarsh and Farr (1969). A detailed comparison of theory and experiment is made.

An analysis of spin-polarization in low energy elastic scattering electrons by one electron s-state atoms is carried out allowing both for electron exchange and relativistic effects. First the collision matrix is written in terms of the asymptotic form of the solutions of the radial equations. Then arguments, based on the invariance of the Hamiltonian under time reversal, space rotation and space reflection are used to write down the most general form of this matrix. It is found that it can be expressed in terms of six independent amplitudes. Then expressions for the observable quantities, including the spin polarization of the electron and of the atom after the collision are derived. Finally, the analysis is specialized to the case where spin-polarization effects are caused by a spin-orbit interaction and these effects are considered in the neighbourhood of cusps and resonances in electron alkali atom scattering.

It is proved that if a scaling parameter alpha contained in suitably chosen trial functions F_1T and F_2T is optimized using Kohn's variational principle, then the virial theorem is satisfied by the optimized variational functions and the variationally determined scattering amplitude. A generalization of the theorem to arbitrary values of the scaling parameter is also established. In addition the virial theorem for the scattering amplitude is applied to the elastic scattering of electrons by atomic hydrogen.

For pt. IV see abstr. A877 of 1974. Inclined beams of electrons and H₂⁺ ions have been used in measurements of dissociative recombination cross sections of H₂⁺ for interaction energies between 0.33 and 4 eV. It was estimated that the absolute accuracy of the results was about +or-10% and the energy resolution ranged from 0.15 to 0.30 eV. The ions are believed to have had the initial distribution of vibrational states measured by von Busch and Dunn (1972). The cross section fell from 2.2*10^-15 cms² at 0.33 eV to 1.9*10^-16 cm² at 4 eV.

The average velocities and energies of ions through a gas in almost perpendicular electric and magnetic fields are calculated. The electric field is taken to be strong enough to give ion energies of a few eV or more, but the magnetic field strength is arbitrary. Symmetric charge exchange is taken to be the most important type of ion collision, and the average initial energy and mean distance moved by the fast neutrals so formed are also briefly discussed. Ion-ion Coulomb collisions and elastic ion-neutral collisions are included as subsidiary types of collision. Symmetric charge exchange produces a large anisotropy in the ion energy which is reduced by the Coulomb and elastic scattering. Expressions are found for the resulting average ion energy parallel to the magnetic field. Examples show that with ion energies of more than a few eV the parallel energy caused by neutral scattering is less than a few percent of the total average energy.

The formation of He⁺(2S) metastable ions by one-electron capture in passage of 10-60 keV ³He²⁺ ions through He, Ar, Kr, H₂, N₂ and O₂ has been investigated. The fast He⁺(2S) ions were detected by recording the 304 AA radiation emitted during electric field quenching of the metastable state. Studies of the yield of He⁺(2S) ions formed as products of single collisions have been used to obtain He⁺(2S) formation cross sections in the different targets with a relative accuracy of +or-10%. Absolute cross sections, believed to be accurate to within a factor of two have been derived from an approximate calibration of the 304 AA radiation detector. Total cross-sections for both one-electron and two-electron capture have also been measured and compared with the He⁺(2S) formation cross sections. The growth of He⁺(2S) atoms from ³He²⁺ beams as the target thickness is increased has also been investigated in hydrogen, argon and krypton. The maximum fractional yield of He⁺(2S) ions observed was 2.5%.

Electron capture into ionized states of fast ions (H⁺, H₂⁺, He⁺) in carbon and gold foils is investigated. Velocity of ejected electrons are measured in the forward direction and a characteristic cusp-shaped peak is found for electrons ejected with velocity equal to that of the incoming ions. The spectra are interpreted by a theory of charge exchange to the continuum, based on an atomic physics ion-atom collision model. As with proper charge exchange, a second order Born approximation is necessary to calculate the high energy cross sections.

Detailed studies on the electron impact dissociation of the HeH⁺ molecular ion produced by the x¹ Sigma to A¹ Sigma transition have been made using the Born-Oppenheimer approximation. For these calculations, accurate Harris-type elliptic orbitals for the electronic states of HeH⁺ ion have been used, which include the effects of distortion polarization due to the heteronuclearity of the ion. The angular distribution of the dissociation fragments and the total dissociation cross section have been computed as functions of the incident electron energy. The results obtained show no striking feature due to the heteronuclearity of the molecular ion. Suggestions for further work in this line are given.

The diffusion coefficients of binary mixtures of argon with the first five members of the alkane series have been determined. The measurements were performed at atmospheric pressure, in the temperature range 300-700K, by means of an improved chromatographic method. The uncertainty in the absolute values of the diffusion coefficients is estimated as +or-2%. The diffusion coefficient measurements for the two geometric isomers of butane in argon have been performed in such a way as to allow direct determination of their ratio with an uncertainty of +or-2%. The results have been employed to examine the regularities in diffusion coefficients of homologous species in mixtures with a common gas. In addition, it is shown that the cross-section of iso-butane in collision with argon is greater than that for normal butane at the same temperature. This result is in opposition to the expectation from a current theory.

Comparison of experimental and theoretical Stark profiles of the allowed 2¹P-3¹D helium line at 6678AA and of the forbidden 2¹P-3¹P component at 6632AA are carried out. The calculated allowed and forbidden lines show good agreement with the experimental data. A study of some other theoretical profiles of this transition, which were previously determined, is performed to ascertain the reasons why poor agreement is found for these profiles when they are compared to the same experimental results.