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Universität zu Köln
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Mathematisch-Naturwissenschaftliche Fakultät
Fachgruppe Physik

I. Physikalisches Institut

On Carbon Clusters

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In the last decade the combination of infrared and visible spectroscopy of mass-selected matrix isolated clusters and high resolution infrared gas phase absorption spectroscopy has made crucial contributions to characterize the structure and dynamics of small carbon clusters. High level ab initio calculations have been applied to this new class of molecules, leading to a better prediction of their chemical and physical properties. Furthermore carbon containing chain molecules as well as pure carbon chains have been found in the interstellar medium.

Small pure carbon clusters have been found as important constituents in a variety of extrasolar sources, such as the tails of comets, shells of late type comets and in star forming regions of interstellar clouds. On the other hand, interstellar dust grains are believed to consist in their nucleus of huge conglomerates of carbon and silicon.

Pure carbon chain molecules are non-polar and thus display no rotational spectrum. They can, however, be detected by their IR-active modes, two of which can principally supply the spectroscopic information via ro-vibrational spectra:

  • the antisymmetric stretching modes, which for the pure carbon chains covers a portion of the IR region, i.e. the inverse wavelength region from about 1700 to 2400 cm-1 and
  • the low bending modes, which occur from about 10 to 150 cm-1

By tunable diode laser spectroscopy the antisymmetric stretching transitions can be recorded. But combination bands of both types of vibrational modes are infrared active and their measurements support the search for the low bending modes.

 

Possible Cluster structures Carbon Clusters are predicted to be linear up to a number of 10 atoms and cyclic up to 30 atoms. For larger Clusters cage strucutres (like the shown buckyball) are predicted to be energetically favourable.