Spectroscopic studies of NaCs for the ground state asymptote of Na plus Cs pairs

The ground state X(1)Sigma(+) of NaCs was studied by laser induced fluorescence Fourier-transform spectroscopy. An accurate potential energy curve was derived from more than 5000 transitions. This potential reproduces the experimental observations within their uncertainties of +/-0.003 cm(-1) and covers about 99.97% of the potential well depth. Few vibrational levels of the shallow state a(3)Sigma(+) below the atomic ground state asymptote were observed. The identification is mainly done by the observed and quantitatively interpreted molecular hyperfine structure applying atomic parameters of the ground states of Na and Cs. An estimated potential curve for a(3)Sigma(+) is reported which can be used together with that of X(1)Sigma(+) for coupled channel calculations of cold collisions between Na and Cs. An example is given.