Theoretical investigation of the cyclopropene radical cation c-C3H+• 4: structure, energetics and spectroscopic properties†

The structure and properties of the cyclopropene radical cation c-C3H+• 4 are investigated by means of quantum chemical methods. The equilibrium geometry of c-C3H+• 4 is found to have C 2 symmetry and a low barrier of 470 cm−1 for stereomutation (around 700 cm−1, including ZPVE corrections) with a transition state of C 2v symmetry. The adiabatic ionisation potential is estimated to be 77,800 cm−1 with respect to c-C3H4. Vertical ionisation potential energies of c-C3H4, and vertical excitation energies to low-lying excited states of c-C3H+• 4 are presented.