Department of Chemistry, Malek-ashtar University of Technology, Shahin-shahr P.O. Box 83145/115, Islamic Republic of Iran
Department of Chemistry, Isfahan University of Technology, Isfahan 84156-83111, Islamic Republic of Iran
Faculty of Chemistry, University of Mazandaran, P.O. Box 453, Babolsar, Islamic Republic of Iran
Infrared (IR) and ultraviolet (UV) spectroscopic analysis of eight structural isomers of C20 carbon nanostructures, i.e. ring, tadpole, bow-tie, dumb-bell, spiro, propellane, bowl and cage, were performed at different levels of theory including semi-empirical (AM1 and PM3), Hartree-Fock (HF/6-31++G, 6-31++G**) and density functional theory (B3LYP/6-31++G, 6-31++G**). A broad range of IR spectra (400-2700 cm-1) is covered by C-C bending vibrations (low frequency region) and C-C stretching vibrations (high frequency region) in almost all isomers. The absorption maximum (λmax) in UV spectra for bowl and cage isomers appears below 300 nm and for cyclic isomers above it. These results show that IR and UV spectra are useful tools for identification of C20 structural isomers.