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XUV photodesorption of carbon clusters ions and ionic photofragments from a mixed methane-water ice

Abstract

The photochemical processing of a CH4:D2O 1:3.3 ice mixture adsorbed on a HOPG surface in the XUV regime has been investigated using pulses obtained from the Free-electron LASer in Hamburg (FLASH) facility. The ice films were exposed to femtosecond pulses with a photon energy of hν = 40.8 eV, consistent with the HeII resonance line. Cationic species desorbing directly from the ice film were detected using time-of-flight (ToF) mass spectrometry. Simple ions formed through the fragmentation of the parent molecules and subsequent recombination reactions were detected and are consistent with efficient D+ and H+ ejection from the parent species, similar to the case for low energy electron irradiation. The FEL fluence dependencies of these ions are linear or exhibit a non-linear order of up to 3. In addition, a series of Cn+ cluster ions (with n up to 12) were also identified. These ions display a highly non-linear desorption yield with respect to the FEL fluence, having an order of 6-10, suggesting a complex multi-step process involving the primary products of CH4 fragmentation. Two-pulse correlation measurements were performed to gain further insight into the underlying reaction dynamics of the photo-chemical reactions. The yield of the D2O derived products displayed a different temporal behaviour with respect to the Cn+ ions, indicating the presence of very different reaction pathways to the two families of ionic products.

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Publication details

The article was received on 09 Jan 2018, accepted on 08 Feb 2018 and first published on 08 Feb 2018


Article type: Paper
DOI: 10.1039/C8CP00171E
Citation: Phys. Chem. Chem. Phys., 2018, Accepted Manuscript
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    XUV photodesorption of carbon clusters ions and ionic photofragments from a mixed methane-water ice

    T. Suhasaria, J. Thrower, R. Frigge, S. Roling, M. Bertin, X. Michaut, J. FILLION and H. Zacharias, Phys. Chem. Chem. Phys., 2018, Accepted Manuscript , DOI: 10.1039/C8CP00171E

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