On the large organic molecules in the interstellar gas

Abstract

It is argued that polycyclic aromatic hydrocarbons (PAHs) are not the dominant large molecules in the interstellar gas because (i) the known interstellar molecules are more general in structure and composition; (ii) none of the many infrared and optical interstellar features attributed to large molecules has yet been assigned to a specific PAH; (iii) the PAH hypothesis fails to offer a credible interpretation of the diffuse interstellar bands, and (iv) PAHs tend to accrete carbon in the diffuse interstellar gas at an unacceptably high rate. An alternate scheme is proposed in which a stable population of long carbon chains and large planar rings is maintained by C+ insertion, photocleavage, and spontaneous isomerization.Chains with 20–30 atoms are synthesized at about the right abundance to account for the diffuse bands, and it is suggested that these and derivative rings of comparable size or slightly larger are the dominant large molecules in the diffuse gas. It is also suggested that in a a slower subor...