Anharmonic Force Fields of Naphthalene-h 8 and Naphthalene-d 8

Abstract

The cubic and the quartic semidiagonal anharmonic force fields of naphthalene-h8 and -d8 are obtained using density functional theory (DFT) with the B9-71 functional and a triple-zeta plus double polarization (TZ2P) basis set. The fundamental frequencies computed by second-order vibrational perturbation theory are in very good agreement with the experimental data, with a mean absolute deviation (MAD) of 4 cm(-1) for C(10)H(8) and 6 cm(-1) for C(10)D(8). Some of the fundamental frequencies have been reassigned on the basis of the present results. Only CH stretchings seem to be significantly affected by Fermi resonances, with two shifts larger than 10 cm(-1). Calculated infrared harmonic intensities reproduce the experimental data within 15%, with the exception of CH stretchings affected by a larger error. Scale factors from C(10)H(8) have been tested by deriving the fundamental frequencies of C(10)D(8) from the theoretical harmonic ones. These fundamentals are in nice agreement with those obtained from the C(10)D(8) anharmonic force field. These results support the use of scale factors to calculate the vibration spectra of larger polycyclic aromatic hydrocarbons of great astrophysical interest.