Fourier-transform spectroscopy of (4)1Σ+ → A 1Σ+ − b 3Π, A 1Σ+ − b 3Π → X1Σ+, and $(1)^3\Delta _1\rightarrow b{\,}^3\Pi _{0^\pm }$(1)3Δ1→bΠ±3 transitions in KCs and deperturbation treatment of A 1Σ+ and b 3Π states

Abstract

High resolution Fourier-transform spectroscopy data of term values in the spin-orbit (SO) coupled first excited A 1Σ+ and b 3Π states in KCs were obtained from (4)1Σ+ → A 1Σ+ − b 3Π, A 1Σ+ − b 3Π → X1Σ+, and $(1)^3\Delta _1\rightarrow b{\,}^3\Pi _{0^\pm }$(1)3Δ1→bΠ0±3 spectra of laser-induced fluorescence (LIF). About 3000 new rovibronic term values of the A 1Σ+ and $b{\,}^3\Pi _\Omega$b3ΠΩ states were obtained with an uncertainty about 0.01 cm−1 and added to the previously obtained 3439 term values in Kruzins et al. [Phys. Rev. A 81, 042509 (2010)] and 30 term values of the $b{\,}^3\Pi _{0^+}$b3Π0+ state levels below the A 1Σ+ state in Tamanis et al. [Phys. Rev. A 82, 032506 (2010)]. The data field was extended considerably, going down to vibrational level vb = 0 and up in energy to 13 814 cm−1, as compared to previously achieved vb = 14 and E = 13 250 cm−1. Overall 6431 e-symmetry term values of 39K133Cs were included in 4 × 4 coupled-channel deperturbation analysis. The analytical Morse-Long-Range (MLR) function yielded empirical diabatic potentials for the A 1Σ+ and $b{\,}^3\Pi _{0^+}$b3Π0+ states while the morphing of the SO ab initio points [J. T. Kim et al., J. Mol. Spectrosc. 256, 57 (2009)] provided the empirical diagonal and off-diagonal SO functions. Overall 98.5% of the fitted term values were reproduced with a rms (root mean square) uncertainty of 0.004 cm−1. The reliability of the model is proved by a good agreement of predicted and measured term values of the 41K133Cs isotopologue, as well as of measured and calculated intensities of (4)1Σ+ → A 1Σ+ − b 3Π LIF progressions. Direct-potential-fit of low-lying vb levels of the $b{\,}^3\Pi _{0^-}$b3Π0− component yielded the MLR potential which represents the 204 f-symmetry experimental term values with a rms uncertainty of 0.002 cm−1. The Ω-doubling of the b 3Π0 sub-state demonstrates a pronounced vb-dependent increase.