Abstract
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.
Highlights
(solid black line) is coupled around the inner turning point of the triplet potential a3 + to a level in the excited singlet state B1
It is striking to see in both columns that, in contrast with the generally accepted picture of such a coupling case, the components exhibit clear irregular features resulting from the hyperfine coupling even at short internuclear distances, i.e. well inside the region where the atomic states decouple into triplet and singlet states
By analyzing PA rates of LiCs molecules in the B1 state we find that the formation rate of ground state molecules is governed by a perturbation of the ground state scattering wave
Summary
Details of the experimental setup for the formation and detection of ultracold LiCs molecules have already been described in [18, 20, 22]. In PA, a colliding pair of atoms absorbs a photon resonant to a transition into a bound excited molecular level [25, 26]. For this process we use up to 500 mW of light from a tunable Ti:Sa laser. For the detection of ground state molecules, we use a pulsed dye laser with a repetition rate of 20 Hz (typical pulse energy 8 mJ and beam diameter ∼5 mm). We detect PA resonances by ionizing ground state molecules produced after spontaneous decay from the photoassociated, electronically excited molecules. Ground state molecules formed after PA via intermediate vibrational levels v 9 and v are detected at 859.4 cm−1, a REMPI. It is very likely that highlying levels in the electronic ground state X1 + are ionized at this energy through a broad band of levels in different electronic states between the asymptotes Li(22S1/2) + Cs(62P3/2) and Li(22S1/2) + Cs(52D3/2)
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