C S Singh

On the variable-charge Coulomb-projected Born approximation

Total cross-sections for electron impact excitation of 11S – 23S transition in helium have been calculated using variable-charge Coulomb-projected Born approximation and also using a distorted wave model in which the prior form of theT-matrix is used. The comparison of the two sets of results enables us to make certain observations about the suitability of the variable-charge Coulomb-projected Born approximation.

Electron impact excitation of hydrogen and helium in Coulomb-projected Born methods

Coulomb-projected Born methods for the theoretical study of electron impact excitation of hydrogen and helium are reviewed. The results obtained by using different forms of Coulomb-projected Born methods are compared with other theoretical and experimental results and analyzed. The inadequacy of the variable charge Coulomb-projected Born approximation (VCCPB)—the most recent form of the Coulomb-projected Born methods—in giving good results in processes where exchange is dominant is discussed in detail. The ‘modified’ VCCPB approximation obtained by modifying the VCCPB method to remove its shortcomings is also discussed and its application to electron impact excitation of 23s state of helium is studied.

The effect of exchange in autoionization processes

The effect of including distortion (with and without exchange) in the wavefunction for the continuum electron while calculating the probability of autoionization of 2s21S. 2s2p1,3P, 2p21D and 2p21S states of He and Li+ has been studied.

Excitation of the lowest autoionising states in alkalis

Total cross sections for electron impact excitation of the lowest autoionising levels in Li, Na and K are calculated in the Glauber approximation. Similar calculations are also performed in the first Born approximation as well as using the method of Crothers and McCarroll (1965). The results obtained from these various approximations are compared with earlier theoretical work.

Electron impact excitation of 11 S–21 S transition in helium

The modified variable-charge Coulomb-projected Born approximation is applied to electron impact excitation of 11S–21S transition in helium. The results are compared with other theoretical and experimental results.

Theoretical calculation of electron-impact resonance excitation of alkali atoms

Total cross-section for electron impact excitation of the resonance levels in Li, Na and K are calculated using the method due to Crothers and McCarroll. The results are compared with other available theoretical and experimental data.