Fourier-transform spectroscopy and relativistic electronic structure calculation on the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si28.svg"><mml:mrow><mml:msup><mml:mi>c</mml:mi><mml:mn>3</mml:mn></mml:msup><mml:msup><mml:mstyle mathvariant="normal"><mml:mi>Σ</mml:mi></mml:mstyle><mml:mo>+</mml:mo></mml:msup></mml:mrow></mml:math> state of KCs

The Ti:Saphire laser operated within 13800 - 11800 cm$^{-1}$ range was used to excite the $c^3\Sigma^+$ state of KCs molecule directly from ground $X^1\Sigma^+$ state. laser-induced fluorescence (LIF) spectra $c^3\Sigma^+ \rightarrow a^3\Sigma^+$ transition were recorded with Fourier-transform spectrometer 8000 10000 range. Overall 673 rovibronic term values belonging both $e/f$-components $c^3\Sigma^+(\Omega=1^{\pm})$ $^{39}$KCs, covering vibrational levels $v$ = 0 about 45, and rotational $J\in [11,149]$ determined accuracy 0.01 cm$^{-1}$; among them 7 for $^{41}$KCs. experimental $v\in [0,22]$ involved in a direct point-wise potential reconstruction state, which takes into account $\Omega$-doubling effect caused by spin-rotational interaction nearby $c^3\Sigma^+(\Omega=0^-)$ analysis interpretation facilitated fully-relativistic coupled cluster calculation energy curves $B^1\Pi$, $c^3\Sigma^+$, $b^3\Pi$ states, as well spin-forbidden $c-X$ spin-allowed $c-a$ dipole moments; radiative lifetimes vibronic branching ratios calculated. A comparison relative intensity distributions measured LIF progressions their theoretical counterparts unambiguously confirms assignment suggested [\emph{J. Szczepkovski, et. al.}, JQSRT, \textbf{204}, 133-137 (2018)].