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\maketitle The NaCs molecule is one of the prospective objects forproduction of ultracold polar molecules. LIF Fourier transform spectroscopy study is presented for the (1,3)$\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Pi$ states with 0.03 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ resolution. Potential energy curves (PECs) are obtained by the Inverted Perturbation Approach reproducing (3)$\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Pi$ state}, \underline{\textbf{124}}, 174310, 2006.} energies for $\backslash emphR$ = 3 to 11 {\AA}. In the B(1)$\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Pi$ state we accounted for numerous B(1)$\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Pi \sim c3\Sigma +$ perturbations by omitting perturbed levels for the fit to construct the PEC for $\backslash emphR$ = 2.6 to 8.4 {\AA}. The permanent electric dipole moments $\backslash emphd$ and the $\Lambda$-splitting were measured}, \underline{\textbf{124}}, 184318, 2006.} by dc Stark mixing and electric RF-optical double resonance methods yielding $\backslash emphd$ within 5 - 8 D for (3)$\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Pi$ and $\backslash emphd\sim$ 1 D for the D(2)$\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Pi$ ( 3) state. The radiative lifetimes $\tau$ were measured from LIF kinetics as $\tau$ = 29 to 21 ns for (3)$\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Pi$ ($\backslash emphv$ = 3 to 25) and $\tau$ = 37 ns for D(2)$\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Pi$ ($\backslash emphv$ = 0). The measured data are supported by electronic structure calculations for the (1-3)$\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Pi$ states by many-body multipartitioning perturbation theory of PECs, permanent and transition dipole moments, as well as angular coupling matrix elements for the lowest singlet states. The predicted $\backslash emphd$ values reproduce their experimental counterparts within the measurement errors. Lifetimes for the (1-3)$\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Pi$-states have been calculated in Hund's "a" coupling case using the approximate sum rule over the lower vibronic states. The spectra and formation rates of ultracold NaCs in the $X1\Sigma +$ ($\backslash emphv$ = 0, $\backslash emphJ$ = 0) state were simulated for the optical cycle $a3\Sigma +\to B(1)1\Pi \sim c3\Sigma +\sim b3\Pi \to X1\Sigma +$. The Riga team and the Moscow team acknowledge support by NATO SfP 978029 Optical Field Mapping grant, the Hannover team support by the DFG through the SFB 407.