Antony, J. and von Helden, G. and Meijer, G. and Schmidt, B. (2005) Anharmonic Midinfrared Vibrational Spectra of Benzoic Acid Monomer and Dimer. J. Chem. Phys., 123 (1). 014305.

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Official URL: http://dx.doi.org/10.1063/1.1947191
Abstract
Anharmonic vibrational calculations for the benzoic acid monomer and dimer in the midIR regime (500...1800 cm1) are reported. Harmonic frequencies and intensities are obtained at the DFT/B3LYP level of theory employing D95(d,p) and ccpVTZ basis sets. Anharmonic corrections obtained from standard perturbation theory lead to red shifts of 1...3 %. In almost all cases, the resulting frequencies deviate by less than 1 % from previous measurements [ Bakker et al., J. Chem. Phys. 119, 11180 (2003)]. Calculated intensities are in qualitative agreement with the absorption experiment, with the ccpVTZ values being superior to the D95(d,p) ones for a few modes of the dimer. The antisymmetric outofplane bending mode of the dimer, which is strongly blueshifted with respect to the monomer frequency, represents a remarkable exception: The harmonic frequencies obtained for the two basis sets differ notably from each other, and the anharmonically corrected frequencies deviate from the experimental value by 8 % (D95(d,p)) or 3 % (ccpVTZ). Nonperturbative calculations in reduced dimensionality reveal that the relatively small total anharmonic shift (few tens of cm1) comprises of partly much larger contributions (few hundreds of cm1) which are mostly canceling each other. Many of the individual anharmonic couplings are beyond the validity of second order perturbation theory based on cubic and semidiagonal quartic force constants only. This emphasizes the need for highdimensional, nonperturbative anharmonic calculations at high quantum chemical level when accurate frequencies of Hatom vibrations in double hydrogen bonds are sought for.
Item Type:  Article 

Subjects:  Mathematical and Computer Sciences > Mathematics 
Divisions:  Department of Mathematics and Computer Science > Institute of Mathematics Department of Mathematics and Computer Science > Institute of Mathematics > BioComputing Group 
ID Code:  52 
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Deposited On:  03 Jan 2009 20:20 
Last Modified:  03 Mar 2017 14:39 
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