Resonances in 1s-2s and 1s-2p collision strengths for electron impact excitation of hydrogenic ions

Abstract

Accurate rate coefficients for the electron impact excitation of positive ions are required for the interpretation of the spectra of hot plasmas. In making calculations, account should be taken of resonances in collision strengths at energies which contribute to the rate coefficients. For 1s-2s and 1s-2p excitation of hydrogenic ions it is shown that (3l3l') resonances occur at energies close to the excitation thresholds. The effect of resonances of the type (3ln'l') with n'>or=3 is to increase rate coefficients by about 20% for 1s-2s and 10% for 1s-2p.