Theoretical modeling of the O-H stretching IR bands of hydrogen-bonded dimers of benzoic acid in S-0 and S-1 electronic states

摘要

Theoretical model for vibrational interactions in the hydrogen-bonded dimer of benzoic acid is presented. The model takes into account anharmonic-type couplings between the high-frequency O-H and the low-frequency O center dot O stretching vibrations in two hydrogen bonds, resonance interactions (Davydov coupling) between two hydrogen bonds in the dimer, and Fermi resonance between the O-H stretching fundamental and the first overtone of the O-H in-plane bending vibrations. The vibrational Hamiltonians and selection rules for the C-2h geometry in the S-0 state and for the C-s in-plane bent geometry in the S-1 state of the dimer are derived. The model is used for theoretical simulation of the O-H stretching IR absorption bands of benzoic acid dimers in the gas phase in the electronic ground and first excited singlet states. Ab initio CIS and CIS(D)/6-311++G(d,p) calculations have been performed to determine geometry, frequencies, and excited state energies of benzoic acid dimer in the S-1 state. (c) 2007 American Institute of Physics.