Formation of ultracold LiCs molecules

We present the first observation of ultracold LiCs molecules. The molecules are formed in a two-species magneto-optical trap and detected by two-photon ionization and time-of-flight mass spectrometry. The production rate coefficient is found to be in the range 10(-18) cm(3) s(-1) to 10(-1)6 cm(3) s(-1), at least an order of magnitude smaller than for other heteronuclear diatomic molecules directly formed in a magneto-optical trap.