Short-range Photoassociation of LiRb

We have observed short-range photoassociation of LiRb to the two lowest vibrational states of the $d\,^3\Pi$ potential. These $d\,^3\Pi$ molecules then spontaneously decay to vibrational levels of the $a^3\,\Sigma^+$ state with generation rates of $\sim10^3$ molecules per second. 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 suggests a $p$-wave shape resonance in the scattering 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. These results encourage further work to explain our observed LiRb collisional physics using PECs. 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.