Formation of ultracold, highly polar X1Σ+ NaCs molecules

We present photoassociation spectroscopy of ultracold NaCs molecules formed in a dual-species magneto-optical trap. Excited-state molecules are formed in states correlating to the Na(3S(1/2)) + Cs(6P(3/2)) asymptote. We assign the most prominent observed vibrational progression to the Omega = 2 long range state based on a comparison with ab initio potentials. Molecules are secondarily excited before decaying to deeply bound levels of the electronic ground X-1 Sigma(+) state where they are ionized and detected by time-of-flight mass spectroscopy.