Jahn-Teller distortions in the radical cations of cyclopropane and allene

The Jahn-Teller distorted equilibrium geometries of the radical cations of cyclopropane and allene have been investigated using the MINDO/2 method. For C3H6+, two different structures of C-2v symmetry with almost equal heats of formation were found. Energy minimisation of C3H4+ yields a structure of D-2 symmetry with a dihedral angle between the CH2 groups of 38 degrees. The theoretical Jahn-Teller splitting for those molecules is compared to the experimental data obtained by photoelectron spectroscopy.