Dresden 2017 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 62: Surface Dynamics
O 62.1: Poster
Dienstag, 21. März 2017, 18:30–20:30, P2-OG2
Photon-induced desorption from interstellar ices using XUV free-electron laser pulses — •John Thrower, Tushar Suhasaria, Robert Frigge, Sebastian Roling, and Helmut Zacharias — Physikalisches Institut, Westfälische Wilhelms-Universität Münster, Germany
Solid state processes occurring on grain surfaces play an important role in the chemistry of the interstellar medium. In dense molecular clouds, the low temperature (ca. 10 K) grains are coated with a layer of H2O dominated ice doped with additional species such as CO, CO2, CH4 and NH3. In photon-dominated regions, as well as in accretion disks, these ices are bathed in a flux of UV photons which can lead to the formation of more complex species as well as promoting desorption.
We have used the XUV pulses (40.8 eV) from the FLASH facility to promote photon-induced desorption from such ice films, namely CO and D2O:CH4, adsorbed at 18 K on a graphite substrate. Desorbing CO molecules were state-selectively detected, revealing that desorbing neutral CO molecules display a relatively low degree of rotational excitation (Trot=160 K) but are vibrationally hot (Tvib∼ 1500 K), suggesting desorption via a CO− intermediate.
Irradiation of D2O:CH4 ice resulted in the desorption of simple ionic fragments from the deposited species, methane recombination products up to C3Hx+, and carbon clusters, Cn, up to n=11. The latter display a highly non-linear (m=5) dependence on the incident laser intensity, permitting investigation of the underlying ultrafast dynamics using two-pulse time-correlated desorption.