ИСТИНА

The challenges of experimental and theoretical molecular spectroscopy are: (a) unambiguous assign the observed transitions; (b) fit the directly sampled energy levels to a quantum mechanical model constructed on the physically meaning molecular parameters (c) make predictions about other spectra within the experimental accuracy and (d) capture the intramolecular dynamics and wave functions behavior that are encoded in intensity distribution of the spectrum. Despite their small size diatomic molecules at high excitation do not demonstrate the simple energy structure and transition intensity patterns following by a conventional adiabatic (Born-Oppenheimer) approximation. Sometimes the transgressions lead to catastrophic changes of the spectrum making the assignment to be unfeasible procedure. Nowadays the advanced deperturbation models (based on couple-channel approach) and highly efficient computation schemes are used to realize more complex quantum mechanical calculation including numerous intramolecular interactions. The success of these procedures depends on both experimental data field and results of state-of-art ab initio calculation involved. The molecular parameters used to fit the experimental line positions and intensities contain insights into molecular structure which concerns non-adiabatic wave function behavior. This information can be more useful than the phenomenological parameters themselves, especially when simplifying assumptions are made and tested. The recent success in the direct deperturbation treatment of the excited alkali diatomic states will be shown as example how to use the often huge body of highly accurate spectroscopic data for obtaining reliable predictions of non-adiabatic structure in a wide excitation energy range and internuclear distance. References 1. H.Lefebvre-Brion, R.W.Field. The spectra and dynamics of diatomic molecules. (Ed. Elsevier), 2004. P.796 2. A.Kruzins, I.Klincare, O.Nikolayeva, M.Tamanis, R.Ferber, E.A.Pazyuk, A.V Stolyarov., Phys. Rev. A, 81, 042509 (2010) 3. V.I.Pupyshev, E.A.Pazyuk, A.V.Stolyarov, M.Tamanis, R.Ferber, Phys. Chem. Chem. Phys. 12, 4809-4812 (2010). 4. A. Kruzins, I. Klincare, O. Nikolayeva, M. Tamanis, R. Ferber, E. A. Pazyuk, and A. V. Stolyarov, J. Chem. Phys., 139, 244301 ( 2013) 5. A. Kruzins, K. Alps, O. Docenko, I. Klincare, M. Tamanis, R. Ferber, E. Pazyuk, A. Stolyarov, J.Chem. Phys., 141, 184309 (2014)