Fourier-transform spectroscopy and potential construction of the (2)¹Π state in KCs

The paper presents an empirical pointwise potential energy curve (PEC) of the (2)¹Π state of the KCs molecule constructed by applying the Inverted Perturbation Approach routine. The experimental term values in the energy range E(v′, J′) ∈ [15 407; 16 579] cm⁻¹ involved in the fit were based on Fourier-Transform spectroscopy data obtained with 0.01 cm⁻¹ accuracy from the laser-induced (2)¹Π → X¹Σ⁺ fluorescence spectra. Buffer gas Ar was used to facilitate the appearance of rotation relaxation lines in the spectra, thus enlarging the (2)¹Π data set and allowing determination of the Λ-splitting constants. The data set included vibrational v′ ∈ [0, 28] and rotational J′ ∈ [7, 274] quantum numbers covering about 67% of the potential well. The present PEC reproduces the overall set of data included in the fit with a standard deviation of 0.5 cm⁻¹. The obtained value of the Λ-doubling constant q = + 1.8 × 10⁻⁶ cm⁻¹ for J′ > 50 and v′ ∈ [0, 6] is in an excellent agreement with q = + 1.84 × 10⁻⁶ cm⁻¹ reported in Kim, Lee, and Stolyarov [J. Mol. Spectrosc. 256, 57-67 (2009)]