Structure and Symmetry of the Benzene Cation

The benzene cation is planar with D6h symmetry in the ground state. This is the conclusion from its first photoelectron spectrum with fully resolved rotational lines (ZEKE photoelectron spectrum). The change in the ring structure on ionization deduced from the rotational parameters is less than predicted by ab initio calculations. The elongation of the ring bonds anticipated for the removal of an electron from a bonding orbital is only about 0.1% and thus approximately five times smaller than assumed from the calculations.