Potential energy surfaces of fluorinated benzene radical cations

Ab initio ROHF, CASSCF, UMP2, and DFT/B3LYP calculations using the standard 6‐31G* basis set have been done to study potential energy surfaces (PESs) of selected fluorobenzene radical cations. The stationary PES points have been located, their types and interrelations have been established, and the PES sections have been constructed. The points of conical intersection of π terms have been determined at the ROHF and CASSCF levels of calculations. An opposite behavior of the intersection point at the increase of calculation level has been revealed for C6H5F+ and 1,3‐F2C6H cations, and for the 1,2,3‐F3C6H cation. In the first case, the intersection point has a tendency to shift to the structure of maximum energy and may disappear at a higher level of calculation. However, the intersection is retained in the case of 1,2,3‐F3C6H , which results in the pseudorotational structure of the PES. A low barrier for pseudorotation found for the 1,2,3‐trifluorobenzene radical cation points out the possibility of revealing the pseudo‐rotation in experimental ESR spectra.