Diffuse interstellar medium organic polymers -: Photoproduction of the 3.4, 6.85 and 7.25 μm features

We discuss the production of a hydrogenated amorphous carbon polymer (a-C:H) via the photolysis of methane at low temperature, resulting in a network made of CH2 and CH3 groups with some contribution of unsaturated bonds (C=C, C=C). This solid provides an excellent fit to the Diffuse Interstellar Medium (DISM) 3.4, 6.85 and 7.25 mum features, as observed either in our Galaxy or towards external galaxies lines of sight. The photoproduction and thus photoresistance of this a-C:H made under conditions that resemble those of the DISM (low temperature, UV field) are relevant for astrophysical applications. The profiles of the absorption bands of this material are closer to the astrophysical ones than any previously reported carbonaceous analogs of the DISM organics.