6533b851fe1ef96bd12a8bf0

RESEARCH PRODUCT

Energy and radiative properties of the (3)Π1 and (5)Σ+1 states of RbCs: Experiment and theory

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We combined high-resolution Fourier-transform spectroscopy and large-scale electronic structure calculation to study energy and radiative properties of the high-lying $(3)^{1}\mathrm{\ensuremath{\Pi}}$ and $(5)^{1}\mathrm{\ensuremath{\Sigma}}^{+}$ states of the RbCs molecule. The laser-induced $(5)^{1}\mathrm{\ensuremath{\Sigma}}^{+},(4)^{1}\mathrm{\ensuremath{\Sigma}}^{+},(3)^{1}\mathrm{\ensuremath{\Pi}}\ensuremath{\rightarrow}A(2)^{1}\mathrm{\ensuremath{\Sigma}}^{+}\ensuremath{\sim} b(1)^{3}\mathrm{\ensuremath{\Pi}}$ fluorescence (LIF) spectra were recorded by the Bruker IFS-125(HR) spectrometer in the frequency range $\ensuremath{\nu}\ensuremath{\in}[5500,10\phantom{\rule{0.16em}{0ex}}000]\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ with the instrumental resolution of 0.03 ${\mathrm{cm}}^{\ensuremath{-}1}$. The rotational assignment of the observed LIF progressions, which exhibit irregular vibrational-rotational spacing due to strong spin-orbit interaction between $A^{1}\mathrm{\ensuremath{\Sigma}}^{+}$ and $b^{3}\mathrm{\ensuremath{\Pi}}$ states was based on the coincidences between observed and calculated energy differences. The required rovibronic term values of the strongly perturbed $A\ensuremath{\sim}b$ complex have been calculated by a coupled-channels approach for both $^{85}\mathrm{Rb}^{133}\mathrm{Cs}$ and $^{87}\mathrm{Rb}^{133}\mathrm{Cs}$ isotopologs with accuracy of about 0.01 ${\mathrm{cm}}^{\ensuremath{-}1}$, as demonstrated in A. Kruzins et al. [J. Chem. Phys. 141, 184309 (2014)]. The experimental energies of the upper $(3)^{1}\mathrm{\ensuremath{\Pi}}$ and $(5)^{1}\mathrm{\ensuremath{\Sigma}}^{+}$ states were involved in a direct-potential-fit analysis performed in the framework of inverted perturbation approach. Quasirelativistic ab initio calculations of the spin-allowed $(3)^{1}\mathrm{\ensuremath{\Pi}},(5)^{1}\mathrm{\ensuremath{\Sigma}}^{+}\ensuremath{\rightarrow}$ (1-4)$^{1}\mathrm{\ensuremath{\Sigma}}^{+}$,(1-3)$^{1}\mathrm{\ensuremath{\Pi}}$ transition dipole moments were performed. Radiative lifetimes and vibronic branching ratios of radiative transitions from the $(3)^{1}\mathrm{\ensuremath{\Pi}}$ and $(5)^{1}\mathrm{\ensuremath{\Sigma}}^{+}$ states were evaluated. To elucidate the origin of the $\mathrm{\ensuremath{\Lambda}}$-doubling effect in the $(3)^{1}\mathrm{\ensuremath{\Pi}}$ state, the angular coupling $(3)^{1}\mathrm{\ensuremath{\Pi}}$-(1-5)$^{1}\mathrm{\ensuremath{\Sigma}}^{+}$ electronic matrix elements were calculated and applied for the relevant $q$-factors estimate. The intensity distributions simulated for the particular $(5)^{1}\mathrm{\ensuremath{\Sigma}}^{+}$;$(3)^{1}\mathrm{\ensuremath{\Pi}}\ensuremath{\rightarrow}A\ensuremath{\sim}b$ LIF progressions have been found to be remarkably close to their experimental counterparts.