A method combining the relativistic multichannel theory with the multichannel quantum defect theory is presented to calculate electron impact excitation. The collision strengths and rate coefficients of U⁹¹⁺ ion are computed with this method. Comparison with the results of R-matrix calculation shows that a) there exists another group of resonances near the excitation threshold; b)with the present method resonance structure can be fully resolved; c)the effective collison strength for 1s-2s transition at low temperiture is almost 20% enhanced by the resonances near the threshold.

Electron-impact excitation collision strength Ω(nl-n'l')(3≤n≤7,4≤n'≤7) among configuration-average levels for the Ni-like Ions Pb⁵⁴⁺, Au⁵¹⁺,Ba²⁸⁺,Mo¹⁴⁺,Ge⁴⁺ have been calcuated systematically using the quasirelativitic distorted-wave methods. In addition, the collision strength in high limit have been calculated. The data for the collision strength or thermally averaged rate coefficient over the whole range of energy or temperature have been evaluated by a least-squares spline fitting procedure. As a result, the collision strength with arbitrary electron energy and rate coefficient with arbitrary temperature can be determined by ten parameters.

Cross section for the excitation of Al¹⁰⁺ ion by electron impact from ground state to 2p,3s and 3p states has been investigated with 2-state does-coupling (2cc) and 5-state close -coupling(5cc) approximations. The indirect coupling effect has been analyzed, comparing with the results of distorted wave approximation, it is found that the coupling effect is less important for 2s-2p transition, but for 2s-3s and 2s-3p transition it should be taken into account.

The problem of the slow convergence has been resolved in partial wave expansion for the excitations of electron-ion collisions, with three approximations including plane wave, coulomb Bethe and equimultiple decrease series. As an example, we have computed some important transitions of Ne-like Ge ion and made comparisons between the results obtained by three approximations. The results slow-that all the three methods are acceptable.