M R H Rudge

The simultaneous excitation and ionisation of helium by electron impact

Calculations for the process of e-+He (1s2 1S) to He+(nl)+2e- where n=2 are presented. The results are very different from previous calculations and show better agreement with experimental measurements of excitation to the 2p state. However, the theoretical calculations have an E-1 In E behaviour for high incident energies E, while the experimental measurements appear to have an E-1 behaviour.

Electron scattering by the hydrogen-halides. I. e--HF collisions

Close-coupling calculations have been performed to study the vibrational and rotational excitation of HF by electron impact in the energy range 0.46-2.0 eV. The differential and total cross sections are found to exhibit strong resonance features in the vicinity of the excitation threshold energies. A comparison with experimental data shows good agreement with the magnitudes of the cross sections, which are exceptionally large, but some of the calculated features are sharper than those experimentally observed. The calculations also show a strong resonance profile below the first vibrational threshold.

Total elastic scattering and spin-change cross sections for collision between alkali atoms

Semi-theoretical potential energy curves for the x1 Sigma and x3 Sigma states of the diatomic alkalis Na2, K2, Rb2, Cs2 and RbCs are presented and compared with other estimates. Using these potential-energy functions calculations of the total elastic and spin-change cross sections have been made. The cross sections are compared with experimental data and with the results of other theoretical calculations.

On the bound states of electron-polar-molecule systems

A variational method is described and used to calculate bound states of an electron-polar-molecule system in which the molecule is regarded as a rigid rotor and its interaction with the electron is described by a cut-off dipole potential. Energies are computed as a function of the dipole moment, cut-off radius and moment of inertia of the molecule.

Photoionisation of barium

The total and partial cross sections for the photoionisation of the Ba(6s2)1S0 ground state are calculated in the wavelength range 1200-2380 AA using a relativistic R-matrix approach based on the Breit-Pauli Hamiltonian. Good agreement with the experimental resonance positions is obtained; the magnitude of the cross section is found to be between five and ten times larger than that measured by Hudson et al. (1970). Calculations of the branching ratio in the wavelength range 1600-1200 AA (where the 6s1/2, 5d3/2,5/2 and 6p1/2,3/2 channels are open) indicate that the 5d states of Ba+ are more highly populated than the 6s ground state or the 6p states in this region.

Electron scattering by lithium fluoride

Calculations of elastic and rotational excitation cross sections for electron scattering by LiF are presented. A model potential is used and the cross sections computed using the close-coupling and a number of other theoretical methods. The accuracy of the various methods is assessed and a comparison with experimental data shows close agreement at an energy of 5.4 eV.

Electron collisions with strongly polar molecules

Calculations are presented of cross sections for rotational excitation by electron impact of the polar molecules LiH (2.31), LiCl (2.79), CsF (3.09), NaCl (3.53), CsCl (4.08) and KI (4.26), where the bracketed numbers denote the permanent dipole moments of the species in atomic units. The behaviour of the cross sections is thus obtained for a range of dipole moments and at energies between 0.25 and 8.0 eV. For some of these species, other theoretical and experimental data have been obtained and a comparison with these shows that there is a considerable disparity between the various differential and momentum-transfer cross sections.

On the variational determination of phase shifts for e--H elastic scattering

A consistent and efficient variational procedure is described and applied to the calculation of s-wave, e--H elastic scattering phase shifts.

On an approximation in scattering theory

An approximation, based on regional trial functions, is used to calculate excitation cross sections between some optically connected states of hydrogen and of the alkalis, lithium, sodium and potassium. The cross sections obtained in this approximation, which is simpler than the Born-Oppenheimer approximation, are compared with other theoretical and with experimental results. On the basis of this comparison it is suggested that the wave functions, on which the calculation is based, may form an acceptable first approximation in a more detailed variational treatment.

Spin effects in e-H ionisation

A comparison is made between Born-exchange calculations and experimental measurements of the interference term in electron-hydrogen-atom ionisation. The corresponding values for He+ are also shown.