Plasma-screening effects on direct 1s->2p(+/-) electron-ion collisional excitation rates in dense plasmas

Plasma-screening effects are investigated on the 1s --> 2p(-) (m = -1) and 1s --> 2p(+) (m = +1) electron-ion collisional excitation rates in dense plasmas. The excitation rates are calculated using the semiclassical excitation cross sections obtained by the classical straight-line trajectory approximation with the nonspherical Debye-Huckel potential. The results show that the ratio of the 1s --> 2p(+) to 1s --> 2p(-) excitation rates is found to be a slowly varying function of the temperature. Including the plasma-screening effects for hydrogenic ions, the ratio is found to be a monotonically increasing function of the parameter (Z(2)Ry/kT)(1/2). However, without the plasma-screening effects, the ratio becomes a monotonically decreasing function. The plasma-screening effects appreciably enhance the 1s --> 2p(-) excitation rates and reduce the 1s --> 2p(+) excitation rates. (C) 1996 American Institute of Physics.