Vibrational spectra of cubane and azacubane: a theoretical study

Optimized geometries and orbital energies of cubane and azacubane are obtained at the ab initio (HF, MP2, CCSD, CCSD-T) and DFT(B3LYP) levels of theory using various basis sets (6-31G**, 6-311G**, 6-311++G**, aug-cc-pvdz). The computed C-C and C-H bond distances are in good agreement with the experimental data. The harmonic frequencies are obtained for the above methods except CCSD-T at their respective optimized geometries and the force field and vibrational spectra are analysed. Probable assignments are proposed for all the fundamentals based on the potential energy distribution.