The Fourier transform spectrometer with resolution of 0.03 cm(-1) was applied to disperse the diode laser induced B(1)(1)Π → X(1)Σ(+) fluorescence spectra of the RbCs molecule in a heat pipe. The presence of buffer gas (Ar) produced in the spectra the dense pattern of collision-induced rotation relaxation lines, thus enlarging the B(1)(1)Π data set, allowing to determine the Λ-splitting constants and to reveal numerous local perturbations. In total, 2664 term values for (85)Rb(133)Cs and (87)Rb(133)Cs in the energy range from 13,770 to 15,200 cm(-1) were obtained with accuracy about 0.01 cm(-1). A pointwise potential energy curve (PEC) based on inverted perturbation approach was constructed in the R-range from 3.35 to 9.00 Å for less perturbed vibrational levels v' ε [0, 35] and compared with ab initio calculations. The data included in the fit were reproduced by present PEC with standard deviation (sd) 0.95 cm(-1). More systematic over rotational levels J(') ε [6, 228] data set was obtained for v' ε [0, 2]. These data were reproduced by the obtained PEC with sd of 0.08 cm(-1). The energy of PEC's minimum Te = 13,746.65 cm(-1), as well as other main molecular constants were determined.
The diode laser induced B(1)(1)Π → X(1)Σ(+) fluorescence spectra of the KCs molecule were recorded by Fourier-transform spectrometer with resolution of 0.03 cm(-1). Buffer gas Ar was used to facilitate appearance of rotation relaxation lines in the spectra, thus enlarging the B(1)(1)Π dataset, allowing one to determine the Λ-splitting constants and to reveal numerous local perturbations. A dataset was systematically obtained for B(1)(1)Π vibrational levels ν(') ∈ [0; 5] nonuniformly covering rotational levels with J(') ∈ [7; 233]. For ν(') ∈ [0; 3], the less-perturbed data of f-components were included in the fit. A pointwise potential energy curve (PEC) based on the inverted perturbation approach, as well as the Dunham coefficients, was obtained and compared with ab initio calculations; in particular, the energy of the PEC's minimum T(e) = 14,044.918(6) cm(-1) was determined. Both approaches allowed us to reproduce the vast majority of data used in the fit with accuracy of 0.02 cm(-1). Tentative molecular constants for several vibrational levels of the near lying C(3)(1)Σ(+) state were estimated.
The paper presents an empirical pointwise potential energy curve (PEC) of the (2)(1)Π 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)(1)Π → X(1)Σ(+) fluorescence spectra. Buffer gas Ar was used to facilitate the appearance of rotation relaxation lines in the spectra, thus enlarging the (2)(1)Π 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)].
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