The radiative lifetime of the 1 D 2 state of Ca and Sr: a core-valence treatment
Journal of Physics B: Atomic and Molecular Physics, 18 (8):
1523 (1985)Abstract
Theoretical studies of the lowest 1 S, 1,3 P and 1,3 D states of calcium and strontium are presented. The excitation energies, dipole-allowed transition moments and the 1 D- 1 S quadrupole moment are studied as a function of the one-particle and molecular orbital bases and level of correlation treatment. Including core-valence correlation significantly reduces the magnitude of the dipole and quadrupole transition moments, producing oscillator strengths that lie within the experimental error bars. On the basis of relativistic effective-core potential calculations, the authors find that, unlike barium, the strontium transition moments are not significantly changed when relativistic effects are included. Spin-forbidden transitions were assumed to occur entirely as a result of the breakdown of LS coupling. The magnitude of the singlet-triplet mixing was determined both by ab initio calculation and from the observed deviations from the Lande interval rule. The calculated 1 D 2 state lifetime for Ca is 3.1+or-0.3 ms, which is in reasonable agreement with the experimental value of 2.3+or-0.5 ms (with an absolute upper bound of 4 ms). The dominant decay mechanism is spin-forbidden dipole-allowed transitions, with only 12\% arising from quadrupole transitions. Similarly for the 1 D 2 state of Sr, the authors compute a radiative lifetime of 0.49+or-0.04 ms with only 2\% of the decay from quadrupole transitions.