Chromium difluoride: Probing the limits of structure determination

CrF2 was studied by combined application of quantum-chemical calculations and gas-phase electron diffraction. Coupled cluster and density functional computations found the ground electronic state to be a quasi-linear 5B2 state, which at linearity correlates with a 5A2 state to become a Renner-Teller 5Πg state. Several low-lying electronic states and the shallow bending potentials of the molecule combined with high-temperature experimental conditions make the single-molecule/single-state approach for the electron diffraction analysis unacceptable for this system. Instead, a multi-state approach was needed to determine the vapor composition and the structure, with the vapor consisting of three electronic states (82% 5B2/5Πg, 12% 5A2/5Πg, 6% 5 Σ g + ).