PREDICTIONS OF SPECTAL SIGNATURES OF FULLERENES - 2ND-ORDER JAHN-TELLER EFFECTS ON THE STRUCTURES OF C-44, C-56, C-68 AND C-92

It is argued that pseudo closed-shell fullerenes (those with two electrons in every occupied bonding orbital but with a bonding LUMO in Huckel theory) often fulfil the conditions for second-order Jahn-Teller distortion. Semiempirical (MNDO, AM1 and PM3) calculations on isomers of C-44, C-68 and C-92 yield optimal structures of C-2 symmetry (C-44) and D-2 symmetry (C-68 and C-92), rather than the maximal possible T symmetry while C-56 and a second C-92 isomer give structures of S-4 rather than the maximal T-d symmetry. The distortions to lower symmetry are accompanied by a smoothing out of inequalities in atomic charge. Tetrahedral (T-d) C-84 has a properly closed shell in Huckel theory and shows no loss of symmetry in a semiempirical calculation. Consequences of the distortions for spectroscopic signatures are discussed.