Photoassociation spectroscopy of cold alkaline-earth-metal atoms near the intercombination line

The properties of photoassociation (PA) spectra near the intercombination line (the weak transition between 1S0 and 3P1 states) of group II atoms are theoretically investigated. As an example, we have carried out a calculation for calcium atoms colliding at ultralow temperatures of 1 mK, 1 μK, and 1 nK. Unlike in most current photoassociation spectroscopy, the Doppler effect can significantly affect the shape of the investigated lines. Spectra are obtained using Ca-Ca and Ca-Ca* short-range ab initio potentials and long-range van der Waals and resonance dipole potentials. The similar van der Waals coefficients of ground 1S0+1S0 and excited 1S0+3P1 states cause the PA to differ greatly from those of strong, allowed transitions with resonant dipole interactions. The density of spectral lines is lower, the Condon points are at relatively short range, the reflection approximation for the Franck-Condon factors is not applicable, and the spontaneous decay to bound ground-state molecules is efficient. Finally, the possibility of efficient production of cold molecules is discussed