Theoretical transition probabilities between the lowest ²S, ²P and ²D states of Na, K, Rb, and Cs

Theoretical transition probabilities between the lowest ²S, ²P and ²D 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 ²P-²S and ²D-²P dipole-allowed transitions. Relativistic effects increase the quadrupole moment of Cs, but less so than in Ba, presumably because the alkali ²D states are more diffuse.