Porphyrins within Interstellar Grains

It is postulated that two main chromophores, the tetrabenzoporphyrins MgTBP and H2TBP are situated within interstellar paraffin grain matrices, plus a small amount of pyridine. This hypothesis is supported by an impressive array of lab spectroscopic data, including a total, so far, of 160 lab and DIB coincidences to +/- 1A. The lab data requires no additional matrix shifts or any other theoretical manipulations for fitting the DIB data. In addition, data by Platenkamp and Canters (1981) of MgTBP in a single crystal of n-octane establishes an additional 27 lab and DIB coincidences (to +/- 1A) for the special case of HD29647 and HD21389 respectively. This increases the number of matching lab/DIB data to a total of 187. The outstanding properties of these tetrabenzoporphyrins are (a) thermodynamic stability: more stable than virtually all other microwave interstellar mini-molecules; (b) overall strong absorption features: f values of order unity. Furthermore, they are well shielded within the crystal grains.