Structure and Vibrational Spectrum of Some Polycyclic Aromatic Compounds Studied by Density Functional Theory. 1. Naphthalene, Azulene, Phenanthrene, and Anthracene^†

The geometry and harmonic frequencies of naphthalene, azulene, phenanthrene, and anthracene have been computed using the Becke three-parameter Lee−Yang−Parr functional (B3LYP) and basis sets of spd and spdf quality. A simple scaling procedure for the harmonic frequencies is proposed that brings computed harmonics to within 10−20 cm-1 or better of experimental fundamentals without resorting to internal coordinate transformations. A complete reassignment of the vibrational spectrum of phenanthrene is proposed, and several reassignments are due for anthracene as well. The assignments of Sellers, Pulay, and Boggs (J. Am. Chem. Soc. 1985, 107, 6487) for naphthalene, and of Kozlowski, Rauhut, and Pulay (J. Chem. Phys. 1995, 103, 5650) for azulene, are largely confirmed.