Electronic structures and geometries of the XF3 (X = Cl, Br, I, At) fluorides.

The potential energy surfaces of the group 17 XF3 (X = Cl, Br, I, At) fluorides have been investigated for the first time with multiconfigurational wave function theory approaches. In agreement with experiment, bent T-shaped C2v structures are computed for ClF3, BrF3, and IF3, while we predict that an average D3h structure would be experimentally observed for AtF3. Electron correlation and scalar relativistic effects strongly reduce the energy difference between the D3h geometry and the C2v one, along the XF3 series, and in the X = At case, spin-orbit coupling also slightly reduces this energy difference. AtF3 is a borderline system where the D3h structure becomes a minimum, i.e., the pseudo- Jahn-Teller effect is inhibited since electron correlation and scalar-relativistic effects create small energy barriers leading to the global C2v minima, although both types of effects interfere. [ABSTRACT FROM AUTHOR]