The structure of the free MnF3 molecule - A beautiful example of the Jahn-Teller effect

A new high-temperature gas-phase electron diffraction analysis of manganese trifluoride, combined with high-level quantum chemical calculations, provides direct geometrical evidence of a Jahn−Teller distortion in a free molecule. The potential energy surface of the molecule was scanned extensively by computation at the SCF level. CASSCF and CASPT2 calculations established that of the many C2v symmetry stationary points on the potential energy surface the lowest energy ones are quintets. The global minimum is a quintet state of 5A1 symmetry. In this planar C2v symmetry structure there are two longer and one somewhat shorter Mn−F bonds, with two bond angles close to 106° and one bond angle of about 148°. The second lowest energy state was of 5B2 symmetry, which turned out to be a transition state with an imaginary b2 (in plane) bending frequency. A constrained planar structure of D3h molecular symmetry has appreciably higher energy than the 5B2 symmetry structure. The experimental data are in complete agree...