EXPERIMENTAL INDICATION OF A NAPHTHALENE-BASE MOLECULAR AGGREGATE FORTHE CARRIER OF THE 2175-ANGSTROM INTERSTELLAR EXTINCTION FEATURE

Experiments where the simple polycyclic aromatic hydrocarbon (PAH) nap hthalene (C10H8) is subjected to the energetic environment of a plasma have resulted in the synthesis of a molecular aggregate that has ultr aviolet spectral characteristics that suggest it provides insight into the nature of the carrier of the 2175 Angstrom interstellar extinctio n feature and may be a laboratory analog. Ultraviolet, visible, infrar ed, and mass spectroscopy, along with gas chromatography, indicate tha t it is a molecular aggregate in which an aromatic double ring (''naph thaalene'') structural base serves as the electron ''box'' chromophore that gives rise to the envelope of the 2175 Angstrom feature. This ch romophore can also provide the peak of the feature or function as a ma ntle in concert with another peak provider such as graphite. The molec ular base/chromophore manifests itself both as a structural component of an alkyl-aromatic polymer and as a substructure of hydrogenated PAH species. Its spectral and molecular characteristics are consistent wi th what is generally expected for a complex molecular aggregate that h as a role as an interstellar constituent.