Influence of a Feshbach resonance on the photoassociation of LiCs

We analyze the formation of ultracold ⁷Li¹³³Cs molecules in the rovibrational ground state through photoassociation into the B¹Π state, which has recently been reported (Deiglmayr et al 2008 Phys. Rev. Lett. 101 133004). Absolute rate constants for photoassociation at large detunings from the atomic asymptote are determined and are found to be surprisingly large. The photoassociation process is modeled using a full coupled-channel calculation for the continuum state, taking all relevant hyperfine states into account. The enhancement of the photoassociation rate is found to be caused by an 'echo' of the triplet component in the singlet component of the scattering wave function at the inner turning point of the lowest triplet a³Σ⁺ potential. This perturbation can be ascribed to the existence of a broad Feshbach resonance at low scattering energies. Our results elucidate the important role of couplings in the scattering wave function for the formation of deeply bound ground state molecules via photoassociation.