Fourier-transform spectroscopy and description of low-lying energy levels in the B(1)1Π state of RbCs

The Fourier transform spectrometer with resolution of 0.03 cm−1 was applied to disperse the diode laser induced B(1)1Π → X1Σ+ 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)1Π data set, allowing to determine the Λ-splitting constants and to reveal numerous local perturbations. In total, 2664 term values for 85Rb133Cs and 87Rb133Cs 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 A for less perturbed vibrational levels v′ ∈ [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′ ∈ [6, 228] data set was obtained for v′ ∈ [0, 2]. These data were reprod...