Photoassociative spectroscopy of ultracold lithium(2)-7 and lithium(2)-6

Abstract

We have obtained high-lying vibrational spectra for the $\rm 1\sp3\Sigma\sbsp{g}{+}$ and $\rm 1\sp1\Sigma\sbsp{u}{+}$ excited states of both $\rm \sp7Li\sb2$ and $\rm \sp6Li\sb2$ via photoassociation of colliding ultracold lithium atoms confined in a magneto-optical trap. Photoassociative spectroscopy of ultracold atoms is a powerful tool for probing molecular states near the dissociation energy that are inaccessible by other methods. For an ultracold lithium vapor, the distribution of unbound ground state energies is so small that precise free-bound spectroscopy is possible. Molecular hyperfine structure is resolved. We calculate accurate dissociation energies for both the $\rm 1\sp3\Sigma\sbsp{g}{+}$ and $\rm 1\sp1\Sigma\sbsp{u}{+}$ excited states of Li$\sb2$. A model potential is constructed from a combination of experimental and theoretical information, and used to assign vibrational quantum numbers. We observe rotational structure and assign rotational quantum numbers.