Force field and assignment of the vibrational spectrum of anthracene: Theoretical prediction

A complete set of force constants and their corresponding scale factors were obtained by fitting the experimental frequencies of naphthalene-d(0) and -d(8) to the ab initio force field obtained at the HF/4-21G level. A recently developed fitting procedure is used for this purpose with a modification. The fitting is extremely successful in producing a force field which reproduces the frequencies within an average deviation of 5.7 cm(-1) for naphthalene-d(0) and 4.0 cm(-1) for naphthalene-d(8) from the experimentally observed fundamentals. The ab initio force constants of anthracene were obtained using the same level of theory and scaled using the scale factors of naphthalene. The earlier assignments were either confirmed or reassigned utilizing the frequencies and potential energy distributions derived from the scaled force field. The agreement between the experimental and predicted fundamentals were excellent for this molecule containing 24 atoms, giving an average deviation of 8.2 cm(-1).