The twin-cage compound C120CH2 has been studied by INDO series methods. The results suggest that the formation of C120CH2 reduces the angle constraint at the three-membered ring of methlyene in C60CH2 and C120CH2 is more stable. The direct connection of the two C60 cages rendered a weak interaction between these two cages. The calculated dipole moment of C120CH2 is 1.856 Debyes. The LUMO energy of C120CH2 is less than zero. Thus we suggest this molecule still has the tendency to accept electrons. The electronic spectrum of C120CH2 has been calculated using INDO/CI method. The spectrum of C120CH2 is analogous to those of the parent C60 and its isoelectronic molecule C120O. The calculated spectrum of C120CH2 has strong peaks at 259nm and 330nm. The absorption at 259nm corresponds to the electronic transition of b2(230)→a2(247) and b1(229)→a1(224). The absorption at 330nm corresponds to the electronic transition of a1(241)→b1(249), a2(239)→ b2(253), b1(233)→a1(248), b1(243)→a1(248) and b1(233)→ a1(244). It is in good agreement with experimental values of 258nm and 328nm. Besides we have also discovered some weak absorptions at 403nm, 450nm, 480nm, 560nm. It has not been reported by the experimental research, and should be the characteristic peak for C120CH2.

Key words: CAGE STRUCTURE, ISOMER, ELECTRONIC SPECTROSCOPY, ELECTRONIC STRUCTURE