Computational studies on C36 and its dimer

The energetics of three competing low-energy isomers of C-36 (D-6h, D-2d and C-2v forms) in their singlet and triplet states were computed at the AM1, HF/3-21G, HF/6-31G* and B3LYP/6-31G* levels. The most stable structure is predicted to be the D-6h isomer with a triplet ground state of (3)A(2u) symmetry. This electronic structure can account for the 'covalent' interactions noted in solid C-36. The dimeric structure with D-2h symmetry was optimized using the AM1 and HF/3-21G methods. Dimerization is calculated to be energetically favorable. Important changes expected due to dimerization in the vibrational and electronic spectra are pointed out. (C) 1999 Elsevier Science B.V. All rights reserved.