Accurate characterisation of the C(3)1Σ+ state of the NaRb molecule

We present a first detailed experimental study of the C(3)(1)Sigma(+) state of the NaRb molecule converging to the Na(3p) + Rb(5s) states of separated atoms. Two different high resolution spectroscopic methods have been applied: the Fourier transform spectroscopy of laser induced fluorescence and the V-type optical-optical double resonance polarization labeling spectroscopy. The entire data field for the C-1 Sigma(+) state of (NaRb)-Rb-85 and (NaRb)-Rb-87 consists of rovibrational levels with v' = 0-64 and J' = 4-123. The data were incorporated into a direct fit of a single potential energy curve to the level energies using the Inverted Perturbation Approach method. As the experimental data extend to the "shelf" region of the potential at large internuclear separations of 8.5 angstrom, the C state's suitability for photoassociation yielding cold heteronuclear NaRb is discussed.