UV photodesorption of methanol in pure and CO-rich ices: desorption rates of the intact molecule and of the photofragments - CNRS - Centre national de la recherche scientifique Accéder directement au contenu
Article Dans Une Revue The Astrophysical journal letters Année : 2016

UV photodesorption of methanol in pure and CO-rich ices: desorption rates of the intact molecule and of the photofragments

Résumé

Wavelength dependent photodesorption rates have been determined using synchrotron radiation, for condensed pure and mixed methanol ice in the 7 -- 14 eV range. The VUV photodesorption of intact methanol molecules from pure methanol ices is found to be of the order of 10$^{-5}$ molecules/photon, that is two orders of magnitude below what is generally used in astrochemical models. This rate gets even lower ($<$ 10$^{-6}$ molecules/photon) when the methanol is mixed with CO molecules in the ices. This is consistent with a picture in which photodissociation and recombination processes are at the origin of intact methanol desorption from pure CH$_3$OH ices. Such low rates are explained by the fact that the overall photodesorption process is dominated by the desorption of the photofragments CO, CH$_3$, OH, H$_2$CO and CH$_3$O/CH$_2$OH, whose photodesorption rates are given in this study. Our results suggest that the role of the photodesorption as a mechanism to explain the observed gas phase abundances of methanol in cold media is probably overestimated. Nevertheless, the photodesorption of radicals from methanol-rich ices may stand at the origin of the gas phase presence of radicals such as CH$_3$O, therefore opening new gas phase chemical routes for the formation of complex molecules.

Domaines

Chimie

Dates et versions

hal-01480739 , version 1 (01-03-2017)

Identifiants

Citer

Mathieu Bertin, Claire Romanzin, Mikhail Doronin, Laurent Philippe, Pascal Jeseck, et al.. UV photodesorption of methanol in pure and CO-rich ices: desorption rates of the intact molecule and of the photofragments. The Astrophysical journal letters, 2016, 817 (2), ⟨10.3847/2041-8205/817/2/L12⟩. ⟨hal-01480739⟩
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