High-precision calculations of electric-dipole amplitudes for transitions between low-lying levels of Mg, Ca, and Sr

To support efforts on cooling and trapping of alkaline-earth atoms and designs of atomic clocks, we performed ab initio relativistic many-body calculations of electric-dipole transition amplitudes between low-lying states of Mg, Ca, and Sr. In particular, we report amplitudes for ^1P_1 --> ^1S_0, ^3S_1, ^1D_2$, for ^3P_1 --> ^1S_0, ^1D_2, and for ^3P_2 --> ^1D_2 transitions. For Ca, the reduced matrix element <4s4p, ^1P_1 ||D|| 4s^2, ^1S_0> is in a good agreement with a high-precision experimental value deduced from photoassociation spectroscopy [Zinner et al., Phys.Rev.Lett., v.85, 2292 (2000)]. An estimated uncertainty of the calculated lifetime of the (3s3p ^1P_1) state of Mg is a factor of three smaller than that of the most accurate experiment. Calculated binding energies reproduce experimental values within 0.1-0.2%.