VIBRATIONAL PROPERTIES OF C-20 ISOMERS, A SEMIEMPIRICAL STUDY

Self-consisent field Hartree-Fock calculations using MNDO, AM1 and PM3 hamiltonians were carried out for the vibrational spectra of the geom etrical isomers of the smallest fullerene cluster, C-20 Comparisons wi th a recent density functional approach brought out similarities and d ifferences among the methods and were in accord with earlier first pri nciples stability ordering of the three ground state isomers: the plan ar cyclic form (the ring), the corannulene form (the bowl), and the cl osed cage fullerene form. Complete vibrational symmetry assignments ar e given for the fullerene and the bowl forms and an approximate groupi ng is presented for the ring isomer. The distribution of all vibration al levels is compared among the three forms and the density functional results for the PM3 method, and schematic infrared spectra are calcul ated for the three C-20 forms.