Table of contents

By treating the mercury atomic ion and the mercury atom as one-electron and two-electron systems respectively, and employing the Coulomb approximation to derive the atomic orbitals, the interaction energies between a Hg⁺ ion and a Hg atom at large nuclear separations have been calculated for the ²Σ_u ground state and the ²Σ_g repulsive state of the Hg₂⁺ molecular ion.

These interaction energies have then been used to calculate semi-classical approximation phase shifts for the elastic scattering of Hg⁺ ions by Hg atoms, from which resonance charge-transfer and diffusion cross sections have been derived. Comparison is made with the results of calculations employing cruder approximations and with the rather meagre experimental data on charge transfer.

Finally, the diffusion cross sections have been used to calculate the mobility of Hg⁺ ions in atomic mercury as a function of temperature. The theoretical mobility curve corresponding to the Coulomb approximation atomic orbitals lies somewhat above the rather uncertain experimental data.

The first Born approximation is used to calculate cross sections for one-electron loss from fast atoms A passing through atomic targets B for the following colliding partners (A, B): (H, He), (He, H) and (He, He). Full account is taken of double transitions and the calculations are performed using length and velocity formulation values of the helium matrix elements. Comparison is made with available experimental data, and for the case (H, He) excellent agreement is obtained at high impact energies. Further experimental measurements are desirable for (He, H) and (He, He).

A partial summation of the Born series for the transition operator, retaining only the contributions from intermediate states on the energy shell, is shown to yield a unitary S matrix and to be equivalent to the use of the first Born approximation for the reaction matrix. For the distorted-wave Born series the results provide an improved approximation for fast (i.e. sudden) molecular collisions.

The resonance charge-transfer cross sections for the collision process He²⁺ + H(1s) -> He⁺(2s, 2p) + H⁺ have been evaluated in the atomic two-state and five-state approximations of the impact-parameter method. Momentum transfer was taken into account by the procedure described by Cheshire in 1967. The total and individual cross sections obtained in the five-state approximation exceed the corresponding cross sections obtained in the two-state approximation.

Using the quantal two-state approximation the cross sections for symmetrical resonance charge transfer between protons and excited hydrogen atoms (with principal quantum number 5 or less) are computed. Allowance is made for the effect of the change in the velocity of relative motion during the encounter. In most cases this correction is appreciable if the impact energy is less than about 2·5 ev.

Symmetrical resonance charge transfer between a proton and an excited hydrogen atom is treated classically, the three constants of the classical motion of the electron in a static two-centre potential being chosen so as to ensure the closest possible match with the relevant quantal states. Approximate allowance is made for the quantal tunnel effect. The derived cross sections are in remarkably good agreement with the corresponding cross sections obtained from the quantal two-state approximation.

The 2s, 2p close-coupling equations for electron scattering by lithium atoms are solved from threshold to 54·4 ev. Both the elastic scattering and the 2s-2p excitation cross sections are evaluated. At very low energies the cross sections are shown to be dominated by resonances. At energies between 1 ev and 10 ev the total cross section can be compared with experiment. Any lack of agreement cannot be explained simply by the slow convergence of the close-coupling approximation. Finally, the spin polarization cross section and the polarization of 2p-2s impact radiation are calculated. Comparison of the latter calculation with experiment is satisfactory.

The binary encounter model incorporating exchange as developed by Vriens is used to calculate the cross sections for the excitation of the first excited singlet and triplet states of Hg, Cd and Zn, and the ionization cross sections for Hg, Cd, Zn, Ca, Mg and Be. For both excitation and ionization a quantal momentum distribution function for atomic electrons is used. The calculations are compared with the available experimental and theoretical results.

Semi-classical calculations are carried out for the processes of associative detachment H + H^- -> H₂ + e and of collisional detachment H + H^- -> H + H + e based upon values of the real and imaginary parts of the complex adiabatic potential computed by Bardsley, Herzenberg and Mandl and upon semi-empirical values derived by Chen and Peacher. The experimental data at high velocities lend support to the theoretical predictions of Bardsley et al., but the argument is inconclusive because of possible non-adiabatic contributions. It is pointed out that it may be possible to resolve the question by an experimental investigation of isotope effects at high velocities.

The spatial growth of pre-breakdown ionization currents at values of E/N (E is the electric field and N the gas number density) within the range from 2·24 × 10^-16 to 11·2 × 10^-16 v cm² was measured for helium, for neon and for eight different helium-neon mixtures with fractional concentrations of neon ranging from 0·05 to 0·95. For neon and all the mixtures the ionization growth was found to be accurately represented by the generalized Townsend equation. Analysis of the results in terms of this equation gave values for the primary ionization coefficient α for neon, which agreed with previously published results, and values of α/N for the mixtures, which showed that as the concentration of helium in neon increased α/N at a given E/N first increased and then passed through a maximum value. The maximum value of α/N can be typically 50% above the value for pure neon, and the concentration at which it occurs depends on the value of E/N. The secondary ionization coefficient ω/α for neon and for mixtures with large fractional concentrations (> 0·56) of neon decreased with increasing E/N, while ω/α for mixtures with small fractional concentrations of neon increased with increasing E/N.

The measured ionization growth in helium showed systematic deviations from a Townsend growth, and the implications of these deviations for the determination of α from measurements of pre-breakdown currents in helium are briefly discussed.

The theory recently given by Saksena and Sharma in 1969 for the thermal conductivity of relaxing non-polar gases has been extended to mixtures involving non-polar polyatomic gases. Calculations have been performed on the systems O₂-He, N₂-He and O₂-N₂. The results obtained are in good agreement with the experimental values.

The lifetimes of the upper and lower excited-state levels in helium for the five known laser transitions have been measured as a function of pressure. The lifetimes are strongly pressure dependent and the lifetime value at the laser operating pressure, used together with other relevant information, provides a qualitative description of laser action on the five lines.

Analysis of incompletely resolved structure and of the head structure in the 0-0 band of system D-X ³Σ_g^- confirms the view that state D is a ³II state. The following constants (in cm^-1) are derived, using previously determined constants for the ground state.

State T₀₀B₀

D ³II₂ 59012·50 0·3073

³II₁ 58725·47 0·3066

³II₀ 58552·05 0·3059

It is suggested that D is the ³II_u Rydberg state of the configuration... (π_g3p)(σ_u4p).