W C Fon

Total cross sections for electron excitation transitions between the 11S, 23S, 21S, 23P and 21P states of atomic helium

The five-state R-matrix calculations of Berrington et al. (1975) on the excitation of helium by electrons have been revised and extended to higher electron impact energies. Inelastic scattering cross sections are presented for all transitions between the 11S, 23S, 21S, 23P and 21P states of helium, and elastic cross sections are presented for the n=2 states.

The 1s-2s and 1s-2p excitation of atomic hydrogen by electron impact

The 1s to 2s and 1s to 2p total and differential cross sections for electron impact excitation of atomic hydrogen are calculated from 13 eV to 300 eV. The 1s-2s-2p close-coupling approximation is used for the low partial waves and the unitarized Born approximation for the high partial waves. At the highest energy up to 500 partial waves are included. The calculated differential cross sections are in quite good agreement with the measurements of Williams and Willis (1975).

Elastic scattering of electrons by atomic hydrogen at intermediate energies

The elastic scattering of atomic hydrogen is calculated using the R-matrix method. Total and differential cross sections are reported in the intermediate-energy region and excellent agreement is found with the experimental measurements of Callaway and Williams (1975). Some calculations were also made at low energies where good agreement was obtained with the experimental measurements of Williams and the accurate variational calculations of Schwartz (1961) and Armstead (1968). Momentum transfer and spin-flip cross sections are also calculated.

Elastic scattering of electrons by atomic hydrogen

The 1s-2p pseudo-state approximation of Burke et al. (1963) is used to calculate the differential cross section for elastic scattering of electrons by hydrogen atoms for electron energies from 1 to 200 eV. The results are compared with recent measurements and calculations.

The 11S to 21S and 11S to 21P excitation of helium by electron impact

The R-matrix method calculations of Berrington et al. (1975) and Fon et al. (1979) are extended to the energy ranges 21.4<E<30 eV and 80<E<or=200 eV for the electron impact excitation of 21S and 21P state of helium. Differential and integrated cross sections for these transitions and the ( lambda , chi ) parameters for the 21P excitation are calculated and compared with the recent theoretical calculations and experimental measurements.

The 11S to 23S and 11S to 23P excitation of helium by electron impact

The R-matrix method calculations of Berrington et al. (1975) and Fon et al. (1978) are extended to the calculation of the integrated and differential cross sections for electron excitation of the ground-state helium atom to the 23S and 23P states in the energy ranges (21.4<or=E<or=30 eV) and (80<or=E<or=200 eV). For intermediate energies (30<or=E<or=80 eV) pseudo-resonances arise which make accurate cross sections difficult to calculate and this region is therefore not considered. The calculations are compared with recent theoretical calculations of the mutual angle with the nuclear charge has been fitted by.

Photoionisation of helium

The photoionisation cross section of helium is calculated including the 1s, 2s and 2p eigenstates and 3s, 3p and 3d pseudostates in an expansion of the 1Se initial and 1P0 final wavefunctions. Good agreement is obtained with experiment and with other theories when the He+ ion is left in its ground state. In addition the position, width and shape of the 2s2p 1P0 autoionisation state is accurately described by the theory. However, while the calculated ratio of the He+ ions left in the 2p state to He+ ions left in the 2s state is in good agreement with recent experiments of Woodruff and Samson (1982), and is consistent with recent experiments of Bizau et al. (1982) there is a serious disagreement with the many-body theory of Chang (1980) close to threshold.

Electron impact ionisation of Ti3

The electron impact excitation of Ti3+ from the 3p63d ground state to terms of the 3p53d2 configuration is calculated using a ten-state R-matrix expansion. Three of these terms lie above the ionisation threshold and this calculation shows that the contribution of excitation-autoionisation from these terms dominates the ionisation cross section over a wide range of energies. The discrepancy between the earlier distorted-wave calculations of Griffin et al. (1982) and the experimental ionisation measurements of Falk et al. (1981) has been largely removed.

Electron excitation functions for the 23S, 21S, 23P and 21P states of helium between the n=2 and n=3 excitation thresholds

The differential cross sections for excitation of the ground state of helium to the 23S, 21S 23P and 21P states is calculated using the R-matrix method of Berrington et al. (see ibid., vol.8, p.1459 (1975)). Results are presented at electron scattering angles of 30, 60, 90 and 120 degrees from the excitation threshold up to about 22.4 eV. The calculations are compared with the absolute differential cross section measurements of Pichou et al. (see ibid., vol.9, p.933 (1976)).

Differential cross sections for the excitation of the ground state of helium to the 2,3,43S, 2,3,41S, 2,3,43P and 2,3,41P states at 29.6 eV

The authors have used the results of a nineteen-state R-matrix calculation to calculate the differential cross sections for the excitation of the ground state of helium to the 2,3,43S, 2,3,41S, 2,3,43P and 2,3,41P states at an electron energy of 29.6 eV. For excitation to the n=2 and 3 states the calculations are compared with the measurements of Trajmar (1973), Hall et al (1973) and Chutjian and Thomas (1975). There is good qualitative agreement between theory and experiment but the quantitative agreement is not so good, though better than any previous calculation.