A theoretical study on electronic structures and spectroscopic properties of cyclopropane in ground and excited states Original Research Article

Electronic structures and spectroscopic properties of cyclopropane in ground and excited states were studied by the density functional theory. Cyclopropane in ground state showed a geometric structure of D3h, while for the first excited states, the symmetry of optimum structure was C2v that exhibited an elongated C–C bond and two shortened ones. Several split vibrational spectroscopic terms for the excited states were predicated on the basis of a comparison with those for ground states of lower symmetry. The extremely small CH2 stretch frequency was closely related to the long C–C bond for the first excited states. The first optical absorption band of cyclopropane was indicated to be associated with the excitations from HOMO 3e′ orbitals to 4a1′ and 4e′ orbitals. The strong absorption bands were calculated as arising from the valence-shell transitions.