First-principles studies of Jahn-Teller effects in vanadium, niobium, and tantalum tetrafluoride molecules: electronic structure, vibronic spectra and radiationless decay dynamics

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Transition-metal tetrahalides are a vast class of highly symmetric molecules for which very few spectroscopic data exist. Exploratory ab initio calculations of electronic potential-energy functions have provided evidence that the tetrafluorides of vanadium, niobium and tantalum exhibit exceptionally strong Jahn-Teller effects in their electronic ground state as well as in their first excited electronic state. In addition, there exist seams of conical intersection of the upper sheet of the ground-state surface with the lower sheet of the excited-state surface. The analytic representation of these multi-sheeted multi-dimensional potential-energy surfaces by Jahn-Teller Hamiltonians requires the development of the theory of the latter beyond the current state of the art. This project aims at the first-principles construction of advanced Jahn-Teller Hamiltonians for the title compounds, using multi-configuration Hartree-Fock and multireference configuration interaction methods with inclusion of spin-orbit coupling. Using these Jahn-Teller Hamiltonians, vibrational spectra of the electronic ground state and electronic spectra of the excited state will be calculated. The timescale of the radiationless deactivation of the excited state via pseudo-Jahn-Teller coupling with the ground state will be explored with time-dependent quantum dynamics methods. These detailed theoretical predictions may stimulate future experimental investigations of the spectroscopy and photophysics of transition-metal tetrahalides.