  We report on two-photon photoassociation (PA) spectroscopy of ultracold
heteronuclear LiRb molecules. This is used to determine the binding energies of
the loosely bound levels of the electronic ground singlet and the lowest
triplet states of LiRb. We observe strong two-photon PA lines with power
broadened line widths greater than 20 GHz at relatively low laser intensity of
30 W/cm$^{2}$. The implication of this observation on direct atom to molecule
conversion using stimulated Raman adiabatic passage (STIRAP) is discussed and
the prospect for electronic ground state molecule production is theoretically
analyzed.
