References on "Force constants of Benzene"
 In addition to the references already cited:
 -P. Pulay, G. Fogarasi, J.E. Boggs, J. Chem. Phys., 74 (1981) 3999
 -H. Guo and M. Karplus, J. Chem. Phys.,89(1988) 4235
 There is one additional important reference for Benzene:
 -A.G. Ozkabak, L. Goodman, J. Chem. Phys.,87(1987) 2564
 The latter can be considered as an "experimental force field"; the
 have submitted recently a review paper, comparing this FF to high level
 ab initio calculations:
 -L. Goodman, A.G. Ozkaback and S.N. Thakur, "A Benchmark Vibrational
 Potential Surface: Ground State Benzene", J. Phys. Chem. , accepted.
 Finally, as pointed out by A. Holder in a previous E-mail, there are no
 scale factors available in the litterature for these type of compounds and
 adapted to Hessians calculated at the semi-empirical level such as AM1 and MNDO.
 We have recently submitted a paper on the subject:
 -N. Rougeau, J.P. Flament, P. Youkharibache; H. P. Gervais, G. Berthier
 "Vibrational Modelling in large Polycyclic Aromatic Hydrocarbons"
 J. Mol. Struct. (Theochem), accepted for publication.
 describing a Scaled Force Field for Benzene and larger polycyclic aromatic
 hydrocarbons (PAH) of astrophysical interest: calculating the Hessian at the
 MNDO level, determining scale factors independently for benzene and naphtalene
 to test their transferability, and using this set of transferable scale factors
 to calculate a scaled Hessian and associated vibrational frequencies.
 The overall agreement between experimental and MNDO-SQM frequencies for
 all molecules in the series (benzene, naphtalene, anthracene, phenanthrene,
 pyrene and coronene) is around 25-30 cm-1.
 Philippe Youkharibache
 internet: youkha[ AT ]
 tel: 619-546-5562