The complete set of 134 isolated-pentagon-rule isomers of C-94 has been first investigated by various quantum-chemical approaches. Twenty low-energy cage structures are computed by the ab initio Hartree-Fock self-consistent field method and hybrid density functional theory treatment. All the methods point out a C-2 species as the system ground state. The computed temperature-dependent relative concentrations under the interisomeric thermodynamic equilibrium evaluated by a combined quantum-chemical and statistical-mechanical treatment, predict two distinct structures (C-s, C-2) as the most thermodynamically populated isomers in the system. This finding agrees quite well with the recently reported experimental observations. (C) 2003 American Institute of Physics.