26 June 2011 to 1 July 2011
Montpellier, France
Europe/Paris timezone

Ion irradiation experiments relevant to the astrophysics ices

30 Jun 2011, 18:05
Entrance hall (Polytech)

Entrance hall


Polytech Université Montpellier II


Mr Christian Fernando MEJíA GUAMáN (PUC Rio)


Methane (CH$_{4}$) and methanol (CH$_{3}$OH) ices are present in various astrophysical environments, from dense molecular clouds to several small objects in the outer solar system, in particular on Saturn satellite Triton and to be a constituent of the icy mantle on interstellar grain [1]. There is a clear lack of information about the phenomena induced by the heavy-ion component of cosmic-rays in the electronic-energy-loss regime. In this work, the chemical and physical effects induced by fast heavy ions irradiation on frozen pure methane and methanol at 15 K are studied. Measurements were performed at the medium energy beam-line of the heavy ion accelerator GANIL (Grand Acc\'el\'erateur National d'Ions Lourds), Caen-France [2]. The analysis was done by infrared spectroscopy (FTIR) during irradiation by 220 MeV $^{16}$O$^{7+}$ ion beam. For the case of methane, the principal molecular species identified as a product after irradiation are: CH$_{3}$, C$_{2}$H$_{2}$, C$_{2}$H$_{4}$, C$_{2}$H$_{6}$ and C$_{3}$H$_{8}$. For methanol ices are: H$_{2}$CO, CH$_{2}$OH, CH$_{4}$, CO, CO$_{2}$, HCO and HCOOCH$_{3}$ other products are identified with ambiguity. Their formation and dissociation cross sections are determined. The cross section of CH$_{4}$ and CH$_{3}$OH and its daughters species follows a power law as a function of the electronic stopping power. It is found that, some daughters species cross sections increase with the electronic stopping power roughly as $\sigma\propto$ $S_{e}^{3/2}$. As astrophysical implication, the $S_{e}^{n}$ power law, where $n\approx3/2$ should be very helpful for predicting the CH$_{4}$ and CH$_{3}$OH formation and the dissociation cross sections for other ion beam projectiles and energies in the ISM rich in hydrocarbons that are continuously bombarded by cosmic rays.

Presentation Materials

There are no materials yet.