On the radiation-induced polymerization of indene: from laboratory study to astrochemical implications

The radiation-induced polymerization of indene with a γ radiation source was studied at different dose rates (1, 2, 4, 6 kGy/h) and absorbed doses up to 400 kGy. The polymerization rate was determined through the thermogravimetric analysis and the spectrophotometric analysis of the irradiated indene solutions. With the two complementary methods the polymerization rates were determined for each dose rate. A mixed polymerization mechanism was ascertained involving either free radicals but also cations. In fact, the mixed mechanism was suggested as well by the n = 0.84 exponent of the dose rate in the polymerization kinetics equation and by the value of the radiation chemical yield G p = G(−M) ≈ 10 3 molecules/100 eV. The infrared spectrum of the radiation-polymerized indene is analogous to the spectrum of a reference TiCl 4 -polyindene. However, the FT-IR spectrum of the former shows a couple of better defined and sharper infrared bands with respect to the latter, indicating a better structural regularity for the radio-polyindene. Since indene has been claimed as one of the potential polycyclic aromatic hydrocarbons (PAHs) present in the interstellar medium, our results suggest that it is likely that indene should be accompanied by -polyindene because of the monomer is very sensitive to the high energy radiation-induced polymerization.