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CH Stretching Vibrational Shift of Benzene Dimer: Consistency of Experiment and Calculation
Author(s) -
Wang Weizhou,
Pitoňák Michal,
Hobza Pavel
Publication year - 2007
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.200700415
Subject(s) - dimer , anharmonicity , chemistry , blueshift , density functional theory , benzene , dispersion (optics) , computational chemistry , molecular physics , crystallography , atomic physics , physics , condensed matter physics , optics , organic chemistry , photoluminescence
Three low‐energy structures of the benzene dimer are investigated by several theoretical procedures (RI‐MP2, CCSD(T), RI‐DFT‐D, DFT/BH&H) covering London dispersion energy. The RI‐DFT‐D and CCSD(T) calculations are used to verify the DFT/BH&H dimer characteristics, as only at this level can anharmonic calculations be performed. It is ascertained that the T‐shaped ( C 2 v ) structure, in which the CH stretching frequency of the proton donor shows a significant blue shift, is not stable at any level of theory. It is either a transition structure or a minimum which is easily transformed into a parallel‐displaced structure or a T‐shaped ( C s ) structure, even at low temperature. Consequently, no blue shift can be detected. On the other hand, the calculated anharmonic IR spectra of the two most stable structures of benzene dimer, namely, the T‐shaped ( C s ) and the parallel‐displaced ones, give rise to a small red (and no blue) shift of the CH stretching vibration. This finding is fully consistent with the experimental results.