Formation of deeply bound ultracold Sr2 molecules by photoassociation near the 1S + 3P1 intercombination line

We predict feasibility of the photoassociative formation of Sr2 molecules in arbitrary vibrational levels of the electronic ground state based on state-of-the-art ab initio calculations. Key is the strong spin-orbit interaction between the c (3)Pi(u), A (1)Sigma(+)(u), and B (1)Sigma(+)(u) states. It creates not only an effective dipole moment allowing free-tobound transitions near the S-1 + P-3(1) intercombination line but also facilitates bound-to-bound transitions via resonantly coupled excited-state levels to deeply bound levels of the ground X (1)Sigma(+)(g) potential, with v '' as low as v '' = 6. The spin-orbit interaction is responsible for both optical pathways. Therefore, those excited-state levels that have the largest bound-to-bound transition moments to deeply bound ground-state levels also exhibit a sufficient photoassociation probability, comparable to that of the lowest weakly bound excited-state level previously observed by Zelevinsky et al. [Phys. Rev. Lett. 96, 203201 (2006)]. Our study paves the way for an efficient photoassociative production of Sr2 molecules in ground-state levels suitable for experiments testing the electron-to-proton mass ratio.