THEORETICAL INFRARED-SPECTRA OF LARGE CARBON CLUSTERS

Harmonic force constant calculations at the MNDO SCF level are reported for 22 polyhedral carbon clusters C(n) (20 less-than-or-equal-to n less-than-or-equal-to 240) and for the reference molecules benzene, coronene, and corannulene. New or revised assignments are suggested for coronene and corannulene. Based on the results for the reference molecules and for C60, MNDO is expected to overestimate the vibrational frequencies of the unknown clusters by 10% and to yield reasonable intensity patterns. Calculated infrared spectra are shown and discussed for 12 carbon clusters, with particular emphasis on those which might be observable spectroscopically. The zero-point vibrational energies and the entropy contributions to the free enthalpy are only of minor importance for the thermodynamic stabilities of different clusters.