STRUCTURE AND STABILITY OF C-13 CARBON CLUSTERS

The electronic energies and geometries of the (1)A(g) ring and the (1) Sigma(g)(+) linear isomers of C-13 have been computed and compared at the HF, MP2 and DFT levels. Previous DFT calculations predicted the ring to be more stable than the linear form by about 20-30 kcal/mol, which is in apparent conflict with a recent experiment by Saykally and co-workers in which only the stable (1) Sigma(g)(+) linear C-13 is detected. We found that the inclusion of the correlation energy at the MP2 level reduces the energy difference to just 6.8 kcal/mol. Thermodynamic analysis gives an estimated ratio of ring to chain to be 64 to 1 at 298.15 K, but 1.4 to 1 at 4000 K in favor of the chain.