Relative Stabilities of C74 Isomers

Relative stabilities of six C₇₄ fullerene cages are evaluated: one species obeying the isolated pentagon rule (IPR), three isomers with a pentagon-pentagon junction, two structures with one pentagon-pentagon pair and one heptagon. The computations are carried out using the Gibbs energy in a broad temperature interval. It is shown that the IPR cage (D_3h symmetry) prevails throughout. As low-lying electronic excited states are possible for the cages, their electronic partition functions are included into consideration. It is argued that for the special conditions of the fullerene synthesis/isolation, the electronic partition function based on the singlet excited states only should better reproduce the experimental population findings. The computations indicate that isolation of other C₇₄ cage, in addition to the IPR isomer, is less likely though not impossible.