On the Empirical Determination of Some Harmonic and Anharmonic Force Constants in Benzene

Abstract

In this work, the problem for the quality of empirically determined harmonic force constants in ground electronic state benzene has been carefully reexamined, for the case when strongly anharmonic vibrations are involved and in particular for the A1g (ν1 and ν2) vibrational system. A numerical procedure, based on a local bond Hamiltonian representation for the C−H stretch system and a symmetrized coordinate treatment for the ν1(C−C) mode, has been described and applied to the determination of the harmonic F1,1, F2,2, and F1,2, and some important (diagonal) anharmonic force constants, instead of the traditional FG analysis. As a reference data for the determination of the required force constants, the set of experimentally observed ν1 and ν2 fundamentals for four D6h benzene species C6H6, C6D6, 13C6H6, and 13C6D6 have been employed. The harmonic force constants as well as harmonic frequencies obtained in this work have substantial deviations from previous determinations. Using the presently determined forc...