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, phenant hrene, and anthracene have been computed using the Becke three-paramet er Lee-Yang-Parr functional (B3LYP) and basis sets of spd and spdf qua lity. A simple scaling procedure for the harmonic frequencies is propo sed that brings computed harmonics to within 10-20 cm(-1) or better of experimental fundamentals without resorting to internal coordinate tr ansformations. A complete reassignment of the vibrational spectrum of phenanthrene is proposed, and several reassignments are due for anthra cene as well. The assignments of Sellers, Pulay, and Boggs (J. Am. Che m. Sec. 1985, 107, 6487) for naphthalene, and of Kozlowski, Rauhut, an d Pulay (J. Chern. Phys. 1995, 103, 5650) for azulene, are largely con firmed.