Hybrid and gradient-corrected density functional theory computations of the cubane infrared and raman spectra

Abstract

The IR and Raman spectra of cubane were computed with three hybrid (B3LYP, B3P86, and B3PW91) and three gradient-corrected (BLYP, BP86, and BPW91) Density Functional Theory (DFT) methods using a 6-31G(d) basis set. The computed CH and CC bond distances were in good agreement with experimental data. The closest agreement with the experimental IR and Raman spectra was obtained with the hybrid B3LYP method. The deviation from the experimental frequencies depended on the nature of the vibration. Thus, CCC-bend and CC-stretch vibrations were higher by 10–20 cm −1, CH-wagging vibrations were higher by 50–60 cm −1, and CH-stretch vibrations were higher by 160–170 cm −1 than the experimental values. By including correlation factors, excellent agreement between the B3LYP computed IR and Raman spectra with the experimental data was obtained.