ИСТИНА

Bound, quasi-bound and continuum rovibronic states located near the dissociation threshold play a key role in the formation of stable molecular ensembles in photo-association, magneto-association and stimulated Raman adiabatic passage (STIRAP) of colliding ultracold atoms [1]. The same molecular states are also tightly involved in the contra verse process, namely: photo and collisionally induced the dissociation of molecules normally taking place at the elevated temperature. Laser-induced fluorescence of the so-called non-diagonal electronic transitions combined with a high-resolution Fourier-transform spectroscopy (FTS-LIF) often can provide all three boundbound, bound-quasibound and bound-continuum parts of the molecular spectra, simultaneously. Here we focus on global deperturbation analysis of diatomic states converging to the common atomic limit. The main challenge of the rigorous deperturbation treatment of these mutually perturbed states is based on the issues [2]: (1) all bound, quasi-bound and continuum states should be simultaneously treated within the framework of the exactly same (uniform) quantum-chemical approximation (model); (2) the conventional adiabatic approximation completely breakdowns on the dissociation: non-relativistic states become degenerate; hence, spin-orbit and hyperfine interactions should be taken into accounted explicitly; (3) the last bound levels are localized in the extremely wide range of internuclear distance (R>100-1000 Å) (4) highly accurate ab initio electronic structure calculations are needed to have got the reliable estimates of potential energy curves and non-adiabatic matrix elements of all states treated in a wide range of R. By the example of high-resolution FTS-LIF spectra of KCs [3-5] molecule and sub-Doppler laser spectroscopy of the K2 dimer produced in the molecular beam [6], we demonstrate that the developed coupled-channel deperturbation model which takes into account for spin-orbit coupling effect and Fermi-contact hyper fine interactions can manage to represent both non-adiabatic energies and radiative transition probabilities of the fully mixed electronic states localized near the dissociation threshold with the unprecedentedly high spectroscopic accuracy. This work has been supported by the Russian Science Foundation (grant No. 23-13-00207, https://rscf.ru/project/23-13-00207/). References: 1. E.A. Pazyuk, A.V. Zaitsevskii, A.V. Stolyarov, M. Tamanis, R. Ferber. Russ. Chem. Rev. 84(10):1001 (2015). 2. E.A. Pazyuk, V.I. Pupyshev, A.V. Zaitsevskii, A.V. Stolyarov. Russ. J. Phys. Chem. A 93(10):1865 (2019). 3. I. Klincare, M. Tamanis, R. Ferber, E.A. Pazyuk, A.V. Stolyarov, I. Havalyova, A. Pashov. J. Quant. Spectr. Rad. Trans. 292, 108351 (2022). 4. V. Krumins, A. Kruzins, M. Tamanis, R. Ferber, V. Meshkov, E. Pazyuk, A. Stolyarov, A. Pashov. J. Chem. Phys. 156, 114305 (2022). 5. V. Krumins, M. Tamanis, R. Ferber, A.V. Oleynichenko, L.V. Skripnikov, A. Zaitsevskii, E.A. Pazyuk, A.V. Stolyarov, A. Pashov. J. Quant. Spectr. Rad. Trans. 283, 108124 (2022). 6. St. Falke, I. Sherstov, E. Tiemann, Ch. Lisdat, J. Chem. Phys. 125, 224303 (2006).