Photon- and electron-stimulated desorption from laboratory models of interstellar ice grains

Abstract

The nonthermal desorption of water from ice films induced by photon and low energy electron irradiation has been studied under conditions mimicking those found in dense interstellar clouds. Water desorption following photon irradiation at 250 nm relies on the presence of an absorbing species within the H2O ice, in this case benzene. Desorption cross sections are obtained and used to derive first order rate coefficients for the desorption processes. Kinetic modeling has been used to compare the efficiencies of these desorption mechanisms with others known to be in operation in dense clouds. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3336466

Electron-Promoted Desorption from Water Ice Surfaces: Neutral Gas-Phase Products

“…21,32,38 The data and results presented in this work come as a fortuitous addition to that story in the light of a more thorough review of our data. At this exposure, C 6 H 6 is present as small islands dispersed over the European Spectrometry Systems) with a homemade line-of-sight tube facing the front of the substrate upon which the molecular film is deposited.…”

“…38,42 This would imply that electron-promoted desorption, initiated by cosmic ray interactions in icy grains, could be the primary non-thermal desorption mechanism in cold, dense regions in the ISM. Kimmel and co-workers have thoroughly investigated the chemistry occurring in H 2 O ices deposited on Pt(111) upon irradiation with low energy electrons (e.g.…”

Photo-stimulated desorption from water and methane clusters on the surface of solid neon

“…The mother cluster for each ion can be deduced from the contour pattern which differs from ion to ion. The ion of 16 amu is not O + but 4 CH + because it is observed without water, at the left end of Fig. 5,a, and not observed from pure water (Fig.…”

“…Though these assignments are bold enough, and in addition, the cluster sizes were not exactly determined at this time, it was revealed that a water molecule plays crucial roles in the process. Firstly, one water molecule is essential for the desorption of the ions investigated here except the case of 4 CH + from the isolated CH 4 molecule. Even for the case of 5 CH + and 2 3 C H , + those are likely produced from two adjacent methane molecules, the addition of one water molecule to the cluster is absolutely essential for the desorption of these species.…”

“…Specifically in the interstellar astrophysics [4], it is considered that the ice surface of the interstellar dust provides the stage where a complex organic molecule is synthesized from simple molecules. Dynamics induced by electronic transitions, such as desorption, dissociation, or chemical synthesis, at the water cluster which contains organic molecules have been studied in conjunction with the photochemistry at ice particles in cosmic space and in the atmosphere.…”