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Issue A&A
Volume 423, Number 3, September I 2004
Page(s) L33 - L36
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:200400032



A&A 423, L33-L36 (2004)
DOI: 10.1051/0004-6361:200400032

Letter

Diffuse interstellar medium organic polymers

Photoproduction of the 3.4, 6.85 and 7.25 $\boldmath {\mu}$m features
E. Dartois, G. M. Muñoz Caro , D. Deboffle and L. d'Hendecourt

Institut d'Astrophysique Spatiale, UMR-8617, Université Paris-Sud, Bâtiment 121, 91405 Orsay, France
    e-mail: emmanuel.dartois@ias.u-psud.fr

(Received 25 May 2004 / Accepted 8 July 2004 )

Abstract
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 CH 2 and CH 3 groups with some contribution of unsaturated bonds (C =C, C $\equiv$C). This solid provides an excellent fit to the Diffuse Interstellar Medium (DISM) 3.4, 6.85 and 7.25  $\mu$m 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.


Key words: ISM: dust, extinction, lines and bands

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