Fourier-transform spectroscopy and relativistic electronic structure calculation on the c3Σ+ 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 the ground X-1 Sigma(+) state. The laser-induced fluorescence (LIF) spectra of the (c)3 Sigma(+). a(3) Sigma(+) transition were recorded with Fourier-transform spectrometer within 8000 to 100 00 cm(-1) range. Overall 673 rovibronic term values belonging to both e/f-components of the c(3)Sigma (+) (Omega = 1 +/-) state of (KCs)-K-39, covering vibrational levels from v = 0 to about 45, and rotational levels J is an element of [11, 149] were determined with the accuracy of about 0.01 cm(-1); among them 7 values for (KCs)-K-41. The experimental term values with v is an element of [0, 22] were involved in a direct point-wise potential reconstruction for the c(3)Sigma(+) (Omega = 1(+/-)) state, which takes into account the Omega-doubling effect caused by the spin-rotational interaction with the nearby c(3)Sigma(+) (Omega = 0(-)) state. The analysis and interpretation were facilitated by the fully-relativistic coupled cluster calculation of the potential energy curves for the B-1 Pi, c(3)Sigma(+), and b(3)Pi states, as well as of spin-forbidden c - Xand spin-allowed c - a transition dipole moments; radiative lifetimes and vibronic branching ratios were calculated. A comparison of relative intensity distributions measured in vibrational c -> a LIF progressions with their theoretical counterparts unambiguously confirms the vibrational assignment suggested in [J. Szczepkowski, et al., JQSRT, 204, 133-137 (2018)]. (C) 2021 Elsevier Ltd. All rights reserved.