Ab initio study of dynamical E × e Jahn-Teller and spin-orbit coupling effects in the transition-metal trifluorides TiF ₃, CrF ₃, and NiF ₃

Multiconfiguration ab initio methods have been employed to study the effects of Jahn-Teller (JT) and spin-orbit (SO) coupling in the transition-metal trifluorides TiF ₃, CrF ₃, and NiF ₃, which possess spatially doubly degenerate excited states ( ^ME) of even spin multiplicities (M = 2 or 4). The ground states of TiF ₃, CrF ₃, and NiF ₃ are nondegenerate and exhibit minima of D _3h symmetry. Potential-energy surfaces of spatially degenerate excited states have been calculated using the state-averaged complete-active-space self-consistent-field method. SO coupling is described by the matrix elements of the Breit-Pauli operator. Linear and higher order JT coupling constants for the JT-active bending and stretching modes as well as SO-coupling constants have been determined. Vibronic spectra of JT-active excited electronic states have been calculated, using JT Hamiltonians for trigonal systems with inclusion of SO coupling. The effect of higher order (up to sixth order) JT couplings on the vibronic spectra has been investigated for selected electronic states and vibrational modes with particularly strong JT couplings. While the weak SO couplings in TiF ₃ and CrF ₃ are almost completely quenched by the strong JT couplings, the stronger SO coupling in NiF ₃ is only partially quenched by JT coupling.