Note on electron impact excitation for transition 2s~2 ~1S_0-2s2p ~3P_1 of Be-like isoelectronic sequence

摘要

Relativistic distorted-wave method was used to calculate the electron impact excitation collision strengths for transitions 2s~2 ~1S_0-2s2p ~3P_1 of Be-like isoelectronic ions. The target states were described, respectively, by 10-level, 46-level and 133-level MCDF configuration-expansion. The relativistic continuum orbitals were calculated in the potential field of frozen target-ion charge distribution with semi-classical exchange potential. The influence of the target states on this collision process along the isoelectronic sequence was investigated in the above three MCDF configuration-expansion modes. It was found that the configurations in the n = 3 and the n = 4 complexes have great influence on both the high and the low Z ions but the influence is relatively small for intermediate Z ions. The latter phenomenon was attributed to competition between opposing correlation and relativistic effects on the collision strengths.