Fourier transform spectroscopy, relativistic electronic structure calculation, and coupled-channel deperturbation analysis of the fully mixed $A^1\hat{I}{\pounds }_u^{+}$ and $b^3{\hat{I}}_u$ states of Cs${}_2$

Abstract

The 4503 rovibronic term values belonging to the mutually perturbed $A^1\hat{I}{\pounds }_u^{+}$ and $b^3{\hat{I}}_u$ states of Cs${}_2$ were extracted from laser induced fluorescence (LIF) $A\sim b\to X^1\hat{I}{\pounds }_g^{+}$ Fourier transform spectra with the 0.01 cm${}^{-1}$ uncertainty. The experimental term values of the $A^1\hat{I}{\pounds }_u^{+}\sim b^3{\hat{I}}_u$ complex covering the rotational levels $J\in [4,395]$ in the excitation energy range $[9655,13630]$ cm${}^{-1}$ were involved into coupled-channel (CC) deperturbation analysis. The deperturbation model takes explicitly into account spin-orbit coupling of the $A^1\hat{I}{\pounds }_u^{+}(A{0}_u^{+})$ and $b^3{\hat{I}}_{0_u}^{+}(b{0}_u^{+})$ states as well as spin-rotational interaction between the $\hat{I}\text{c◯}=0$, $1$ and $2$ components of the $b^3{\hat{I}}_{\hat{I}{\text{c◯}}_u}^{+}$ state. The \emph{ab initio} relativistic calculations on the low-lying electronic states of Cs${}_2$ were accomplished in the framework of Fock space relativistic coupled cluster (FSRCC) approach to provide the interatomic potentials of the interacting $A{0}_u^{+}$ and $b{0}_u^{+}$ states as well as the relevant $A\sim b$ spin-orbit coupling function. To validate the present CC deperturbation analysis solely obtained by energy-based data, the $A\sim b\to X(v_X^{\prime \prime })$ LIF intensity distributions were measured and compared with their theoretical counterparts obtained by means of the non-adiabatic vibrational wave functions of the $A\sim b$ complex and the FSRCC $A\sim b\to X$ transition dipole moments calculated by the finite-field method.

13 pages, 13 figures