Toward the detection of pure carbon clusters in the ISM.

The questions of how and in what form that carbon is distributed in the Universe are critical ones for understanding the evolution of dust and planets, and for elucidating the origin of life on Earth and the prospects for discovering it elsewhere in the cosmos. While the abundant CI and CII atoms and CO molecule, which together account for a large fraction of the total carbon budget, have been thoroughly studied in many sources, and a large number of organic molecules have been detected in cold dust clouds, two potentially large reservoirs of carbon remain essentially unexplored. These are the PAH’s and pure carbon clusters. The former are strongly suspected to be important components of interstellar dust, while the latter have essentially been ignored. Most probably, this simply reflects the fact that relatively little information exists regarding the structures, properties, and in particular, on the transition freauencies of pure carbon clusters that would permit their study by astrophysical methods. The work described below’is designed to mitigate these deficiencies through the study of pure carbon clusters (C,) in the size range n=3-20 by high resolution infrared (350-3000 cm-‘) and far infrared (lo-350 cm-‘) laser spectroscopy. The specific goal of this work is to provide a precise inventory of laboratory frequencies and physical properties for these carbon clusters, such that a serious effort can be made to detect them in cold interstellar sources by far-IR astronomy.