Short-range photoassociation of LiRb

We have observed short-range photoassociation of $^7$Li$^{85}$Rb to the two lowest vibrational states of the $d\,^3\Pi$ potential. We have also observed several $a^3\,\Sigma^+$ vibrational levels with generation rates between $\sim10^2$ and $\sim10^3$ molecules per second, resulting from the spontaneous decay of these $d\,^3\Pi$ molecules. This is the first observation of many of these $a\,^3\Sigma^+$ levels. We observe an alternation of the peak heights in the rotational photoassociation spectrum that depends on the parity of the excited molecular state. Franck-Condon overlap calculations predict that photoassociation to higher vibrational levels of the $d\,^3\Pi$, in particular the sixth vibrational level, should populate the lowest vibrational level of the $a\,^3\Sigma^+$ state with a rate as high as $10^4$ molecules per second. This work also motivates an experimental search for short-range photoassociation to other bound molecules, such as the $c\,^3\Sigma^+$ or $b\,^3\Pi$, as prospects for preparing ground-state molecules.