COLLISION STRENGTHS AND RATE COEFFICIENTS FOR ELECTRON-IMPACT EXCITATION IN HE-I - AN EXTRAPOLATION OF R-MATRIX CALCULATIONS TO HIGHER ELECTRON-IMPACT ENERGIES

Extrapolations to higher electron impact energies of collision strengths calculated using the R-matrix method are presented for electric dipole allowed transitions of neutral helium. The extrapolations are based on a spline fit constrained by the high-energy limiting behaviour deduced from the Bethe approximation. This fit allows the calculation of the rate coefficients over a wide temperature range. The possibility of calculating collision rates in a non-equilibrium plasma is also discussed.