  As a result of the search for the identity of the chromophores responsible
for producing the diffuse interstellar bands, a comprehensive exposition of
experimental data is presented, which implicates the following molecules- 1.
The extremely stable organic molecules, magnesium tetrabenzoporphyrin (MgTBP)
and H2TBP. 2. A paraffin matrix (referred to as grains) containing TBPs. 3. A
low concentration of pyridine (also within the grains), whose transmission
window at 2175 Angstroms, accounts for the ubiquitous UV bump. The blue
emission spectra associated with the central star, HD44179, of the Red
Rectangle displays the fluorescence excitation spectra of bare MgTBP. This
unique spectrum matches the low temperature lab data of MgTBP in the vapor
phase. An effective grain temperature of 2.728 K (plus or minus 0.008) was
deduced, based on MgTBPs lowest measured vibrational state of 341 GHz.
