• Leto, Giuseppe
• Strazzulla, Giovanni
• Baratta, Giuseppe
• Fulvio, D.
• Palumbo, Mariaelisabetta
• Ioppolo, S.
• Kanuchova, Z.
• Sangiorgio, I.
• Garozzo, M.

Abstract

Molecules in the solid phase have been detected in the line of sight of quiescent molecular clouds and star forming regions as icy mantles on dust grains. Water (H_2O), carbon monoxide (CO), carbon dioxide (CO_2), methanol (CH_3OH), carbonyl sulfide (OCS), methane (CH_4), ammonia (NH_3) and sulfur dioxide (SO_2)are the most abundant observed species (e.g. Gibb et al. 2004).It is generally accepted that some of these species (such as CO) freeze out from the gas phase while others (such as water and methanol) are formed on grains after surface reactions (Ioppolo et al. 2008). CO_2 and OCS are not expected to freeze out from the gas phase and grain surface models do not account for their observed abundance (Ruffle & Herbst 2001;Garrod et al. 2007).It has been suggested that these molecules are formed after energetic processing (i.e. cosmic ion and UV irradiation) of icy grain mantles (d'Hendecourt et al. 1986; Moore et al. 1991; Palumbo & Strazzulla 1993; Ioppolo et al. 2009; Garozzo et al. 2010 ). Here we will present the results of laboratory experiments which show the formation of CO_2 and OCS after ion irradiation of relevant ice mixture at low temperature (10-20 K). We will also present the comparison between the profile of bands in laboratory spectra with those observed in space.We will show that laboratory spectra well reproduce the interstellar features and that the amount of carbon dioxide and carbonyl sulfide formed after ion irradiation can account for the observed amount towards molecular clouds.

Topics

• impedance spectroscopy
• surface
• Carbon
• grain
• experiment
• forming
• gas phase