Effective collision strengths for optically allowed transitions among degenerate levels of hydrogenic ions with

The Coulomb–Born approximation is used to calculate electron-impact excitation collision strengths and effective collision strengths for optically allowed transitions among degenerate fine-structure levels of hydrogenic ions with 2 ⩽ Z ⩽ 30 and n ⩽ 5 . Collision strengths are calculated over a wide range of energies up to E j / Z 2 = 10 Ryd . Effective collision strengths are obtained over a wide temperature range up to 10 8 K by integrating the collision strengths over a Maxwellian distribution of electron velocities.