  We perform photoassociation spectroscopy in an ultracold $^{23}$Na-$^6$Li
mixture to study the $c^3\Sigma^+$ excited triplet molecular potential. We
observe 50 vibrational states and their substructure to an accuracy of 20 MHz,
and provide line strength data from photoassociation loss measurements. An
analysis of the vibrational line positions using near-dissociation expansions
and a full potential fit is presented. This is the first observation of the
$c^3\Sigma^+$ potential, as well as photoassociation in the NaLi system.
