ON THE STRUCTURE AND VIBRATIONAL FREQUENCIES OF C-24

Several structures of C-24 have been studied using different density f unctional methods. Using the B3LYP (Becke 3-parameter Lee-Yang-Parr) m ethod, fingerprint-quality infrared spectra have been computed for all species. The computed geometries differ substantially from those obta ined at the SCF level due to delocalization effects. Both ''exact-exch ange'' corrections to the exchange functional and the use of different correlation functionals have significant effects on the relative ener getics. Our best calculations indicate that a dodecadehydrocoronene pl anar sheet and a fullerene cage are comparable in energy, followed by a polyacetylenic ring and a bowl structure, At high temperatures, the ring is expected to prevail due to vibrational entropy from many low-l ying vibrations.