Theoretical transition probabilities between the lowest2S,2P and2D states of Na, K, Rb, and Cs

Theoretical transition probabilities between the lowest 2 S, 2 P and 2 D states of the alkali atoms Na through Cs have been computed using near Hartree-Fock quality Slater basis sets. The important core-valence correlation effects are incorporated explicitly by a configuration-interaction procedure. For Cs, the calculations were repeated using a Gaussian basis set so that relativistic effects could be incorporated through an effective core potential procedure. The authors' best calculated electric quadrupole Einstein coefficients are Na(196.3 s -1 ), K(103.6 s -1 ), Rb(72.4 s -1 ) and Cs(19.7 s -1 ). Core-valence effects become increasingly important down the column, and reduce the quadrupole transition strengths to about the same degree as for the 2 P- 2 S and 2 D- 2 P dipole-allowed transitions. Relativistic effects increase the quadrupole moment of Cs, but less so than in Ba, presumably because the alkali 2 D states are more diffuse.