Anti-hydrogen bond in the benzene dimer and other carbon proton donor complexes

Journal of Physical Chemistry A

Volumn 102, Issue 15, 1998, Pages 2501-2504

  Hobza, Pavel ^a   Špirko, Vladimír ^a   Selzle, Heinrich L ^b   Schlag, Edward W ^b  

^a J HEYROVSKÝ INSTITUTE OF PHYSICAL CHEMISTRY   (Czech Republic)

^b TECHNICAL UNIVERSITY OF MUNICH   (Germany)

Author keywords

[No Author keywords available]

Indexed keywords

EID: 11744370264     PISSN: 10895639     EISSN: None     Source Type: Journal    
DOI: 10.1021/jp973374w     Document Type: Article

References (15)

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11. Experimentally the anti-H-bond should be observable as a strong blue-shift of the C-H stretching frequency in the benzene dimer. The isolated benzene dimer is only stable at very low temperatures and can be prepared in supersonic jet experiments. The low concentration under these conditions does allow for direct IR absorption measurements; hence, other experimental techniques have to be applied. Depletion spectroscopy is one, where a strong laser is tuned to the absorption band of this C-H stretching frequency. The absorbed photons will dissociate the dimer and lead to a reduced signal in a subsequent resonance-enhanced multiphoton ionization experiment. At the present, no strong tunable IR lasers at this wavelength range of 3 μm are available, as commercial OPO systems here only extend to 2.6 μm. Other hole-burning techniques such as stimulated Raman spectroscopy with ion detection or stimulated emission pumping of the benzene dimer could give information on the ground-state frequencies but have not yet been employed to study this effect. The shortening of the C-H bond in the isolated dimer cannot be measured directly, as microwave spectra only allow for the determination of the center-of-mass distance between the two benzene rings. Here information should be obtained from solid benzene, but the benzene solid structure is of more herringbone structure, and not a T-shape one. The bond length can be obtained from neutron scattering experiments, as X-ray studies are not sensitive to the hydrogen atoms. We have carefully checked the literature, but to our best knowledge there is no relevant paper available giving any information on the shortening of the C-H bond in the benzene dimer. The same is true for matrix IR experiments.
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