Fourier-transform spectroscopy and global deperturbation treatment of the $A^1{\Sigma }_u^{+}$ and $b^3{\Pi }_u$ states of K${}_2$ in the entire bound energy range

Abstract

Rotationally-resolved Fourier-transform spectra of laser-induced fluorescence (LIF) $A^1{\Sigma }_u^{+}\sim b^3{\Pi }_u\to X^1{\Sigma }_g^{+}$ of K${}_2$ molecules were recorded and analyzed yielding 4053 term values of spin-orbit (SO) coupled $A\sim b$ complex of ${}^{39}$K${}_2$ isotopologue with ca 0.01 cm${}^{-1}$ accuracy. Their compilation with 1739 term values from previously published sources allowed to cover the energy range [9955, 17436] cm${}^{-1}$ from the bottom of the lower-lying $b^3{\Pi }_u$ state up to the vicinity of the atomic asymptote $4s{}^2{\mathrm{S}}_{1/2}$ + $4p{}^2{\mathrm{P}}_{1/2}$, with rotational quantum number $J\in [0,149]$. The experimental data were processed by a direct 6$\times$6 coupled-channel (CC) deperturbation treatment, which accounted explicitly for both SO and electronic-rotational interactions between six states: $A^1{\Sigma }_u^{+}$($0$), $b^3{\Pi }_u$(0,1,2), $c^3{\Sigma }_u$(1), and $B^1{\Pi }_u$(1). The initial parameters of the global deperturbation model have been estimated in the framework of {\it ab initio} electronic structure calculations applying multi-referenced configuration-interaction and coupled-clusters methods. The interatomic potentials analytically defined for $A$ and $b$ states, as well as SO-splitting of the triplet $b$ state and $A\sim b$ SO-coupling functions have been refined to fit 5792 term values of the ${}^{39}$K${}_2$ isotopologue, whereas the rest parameters were fixed on their {\it ab initio} values. The resulting mass-invariant parameters of the CC model reproduced the overall rovibronic term energies of the $A\sim b$ complex of ${}^{39}$K${}_2$ with the accuracy, which is well within the experimental errors. This deperturbation analysis provided the refined dissociation energy $T_{dis}$=17474.569(5) cm${}^{-1}$ and the long-range coefficient $C_3^{\Sigma }$ = 5.501(4) $\times 10^5$cm${}^{-1}$ A${}^3$ relevant to the non-relativistic atomic limit $4s$+$4p$.

18 pages, 11 figures