Production of ultracold heteronuclear YbRb* molecules by photoassociation

We have produced ultracold heteronuclear YbRb${}^{\ast }$ molecules in a combined magneto-optical trap by photoassociation. The formation of electronically excited molecules close to the dissociation limit was observed by trap loss spectroscopy in mixtures of ${}^{87}$Rb with ${}^{174}$Yb and ${}^{176}$Yb. The molecules could be prepared in a series of vibrational levels with resolved rotational structure, allowing for an experimental determination of the long-range potential in the electronically excited state.