Direct deperturbation analysis of the $AΠ2∼BΣ+2$ complex of $LiAr7,6$ isotopomers

Direct deperturbation analysis of the highly accurate experimental rovibronic term values of the $AΠ2∼BΣ+2$ complex of LiAr [R. Brühl and D. Zimmermann, J. Chem. Phys. 114, 3035 (2001)] has been performed in the framework of inverted close-coupling approach implicitly adjusted to the unified treatment of the overall $A∼B$ coupling effect without reducing the rovibrational dimensionality. The nonlinear fitting procedure was supported by the ab initio calculations on the spin-orbit and angular coupling matrix elements between the lowest $XΣ+2$⁠, $AΠ2$⁠, and $BΣ+2$ states. The analytical grid mapping based on the reduced variable representation of the radial coordinate $r$ was used to improve the efficiency of the solution of the close-coupling radial equations near the dissociation limit. The mutual $A∼X$ perturbation effect on the $AΠ2$ term values and spin-rotation splitting of the ground state were evaluated for both $LiAr7,6$ isotopomers. The resulting empirical potential-energy curves for the adiabatic $AΠ2$ and $BΣ+2$ states, along with the refined $r$-dependent nonadiabatic matrix elements, reproduce the total rovibronic structure of the $LiAr7$ complex with the standard deviation of $0.003cm−1$⁠. The mass invariance of the deperturbed electronic parameters was confirmed by the calculation of the rovibronic term values of the $LiAr6$ isotopomer which coincided with their experimental counterparts within $0.004cm−1$⁠.