FORCE-FIELD AND ASSIGNMENT OF THE VIBRATIONAL-SPECTRUM OF ANTHRACENE - THEORETICAL PREDICTION

A complete set of force constants and their corresponding scale factor s 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 devi ation of 5.7 cm(-1) for naphthalene-d(0) and 4.0 cm(-1) for naphthalen e-d(8) from the experimentally observed fundamentals. The ab initio fo rce constants of anthracene were obtained using the same level of theo ry and scaled using the scale factors of naphthalene. The earlier assi gnments 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 we re excellent for this molecule containing 24 atoms, giving an average deviation of 8.2 cm(-1).