Raman spectra of polycyclic aromatic hydrocarbons. Comparison of calculated Raman intensity distributions with observed spectra for naphthalene, anthracene, pyrene, and perylene

Theoretical calculations of Raman spectra have been performed for naphthalene, anthracene, pyrene, and perylene. Normal-coordinate calculations have been carried out by ab initio Hartree-Fock (HF) theory, density functional (DF) theory, and a simple force field model (MO/8 model). Raman intensities have been evaluated for each normal coordinate by the finite field method using polarizability derivatives calculated with the wave functions from HF and DF theories. The calculated vibrational frequencies show good agreement with observed ones within similar to 10 cm(-1) at the BLYP/6-31G* level. Normal coordinates obtained by the MO/8 model generate better intensity distributions than those calculated at the BLYP/6-31G* level; the average deviation factor of intensity ratios, which is defined as an invariant index for discrepancies of intensity distributions between calculation and experiment, is found to be 1.35-1.97 for MO/8 normal coordinates, whereas it is 1.58-5.57 for BLYP normal coordinates. (C) 1998 Elsevier Science B.V.