U sing both INDO/SCI and INDO/SDCI methods, the UV-visibie spectra of C60 have been calculated. The results are in good agreement with experiment, On the basis of cnorrect electronic spectra, calculations of Ihc nonlinear third-order optical suscepti-bility (yijkl) of C60 are reported. The calculations are performed using the INDO/CI melhod combined with a sum-ver-tates expression for yijkl. The calculated resulls, <y>(-ω, ω, -ω, ω)=730×10-34 esu (ω=1.064μm) and <y>(-2ω; ω, ω, 0)=6.90×10 -34 esu (ω=1.91μm), are in good agreement with some of the reeent obserations too.

Intermediate neglect of differential overlap (INDO) calculations were used to study two structures of C60NH+2: one of C2v geometry with a bridging NH+2 across the bond between two fused six-membered rings in C60 and the other of Cs geometry with a bridging NH+2 across the bond between a five-and a six-membered ring, We calculated the most stable isomer o1 C60NH+2 to be of C2v, symmetry. It was found that the C2v isomer has a protonated aziridine structure with a bridging C--C bond length of 0.1520nm. The electronic spectra of both isomers of C60NH+2 were calculated. Comparisons were made with the isoelectronic mniecules C60O and C60CH2, cases in which the calculated electronic spectra for the most stable isomers C60O (C2v) and C60CH2 (Czv) are in good agreement with recent experimental results.

Possible isomers of Buckminsteffullerene derivatives C60O2 and C60O3 are studied with the semiempisical quantum mechanical INDO method. The C60O2 isomer of Cs symmetry, where the epoxy oxygen atoms are on the 6-6 bond of a hexagon, is foued most stable. The C60O3 isomer of C3v symmetry with a single epoxy chain connecting both carbons of a 6-6 bond is most stable. However, the other two isomers of C2 and C, symmetries are near as stable. In all cases, the 6-6 carbon carbon bond in the epoxial ring is not broken. Based on the structures so identified, the calculated electronic spectra of C60O2, and the 13C-NMR analysis of both C60O2 and C60O3 agree well with experiment. he calculated electronic spectra of C60O3 are theoretical prediction. The chemical reactivity of C60O2 and C60O3 is disused in connection with our calculated results.