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          Institute: Fritz-Haber-Institut     Collection: Molecular Physics     Display Documents



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ID: 233612.0, Fritz-Haber-Institut / Molecular Physics
Anharmonic midinfrared vibrational spectra of benzoic acid monomer and dimer
Authors:Antony, Jens; Helden, Gert von; Meijer, Gerard; Schmidt, Burkhard
Language:English
Date of Publication (YYYY-MM-DD):2005-07-01
Title of Journal:The Journal of Chemical Physics
Journal Abbrev.:J. Chem. Phys.
Volume:123
Start Page:014305-1
End Page:014305-11
Copyright:2005 American Institute of Physics
Review Status:Peer-review
Audience:Experts Only
Abstract / Description:Anharmonic vibrational calculations for the benzoic acid monomer and dimer in the mid-IR regime (500–1800 cm⁻¹) are reported. Harmonic frequencies and intensities are obtained at the DFT/B3LYP level of theory employing D95(d,p) and cc-pVTZ basis sets. Anharmonic corrections obtained from standard perturbation theory lead to redshifts 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 cc-pVTZ values being superior to the D95(d,p) ones for a few modes of the dimer. The antisymmetric out-of-plane 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% (cc-pVTZ). Nonperturbative calculations in reduced dimensionality reveal that the relatively small total anharmonic shift (few tens of cm⁻¹) comprises of partly much larger contributions (few hundreds of cm⁻¹) 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 high-dimensional, nonperturbative anharmonic calculations at high quantum-chemical level when accurate frequencies of H-atom vibrations in double hydrogen bonds are sought for.
External Publication Status:published
Document Type:Article
Communicated by:Gerard Meijer
Affiliations:Fritz-Haber-Institut/Molecular Physics
External Affiliations:Freie Universität Berlin, Institute of Mathematics II, Arnimalle 2-6, D-14195 Berlin, Germany
Identifiers:URL:http://scitation.aip.org/getpdf/servlet/GetPDFServ... [only for subscriber]
DOI:10.1063/1.1947191
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