Speaker
Description
Ice-covered dust grains are found in many astrophysically relevant environments, including comets, proto-planetary disks and the interstellar medium, and provide surfaces upon which many of the molecules found in space can be made. These ice-covered dust grains undergo so called processing by bombardment with particles such as atoms and ions, by irradiation with light and by heating (thermal processing). Processing leads to the release of species from the icy surface into the gas phase, where they can undergo reaction to form other molecules, and also to chemical reactions that can lead to the production of complex, pre-biotic, species.
We have undertaken a detailed study of the infrared photodesorption of astrophysically relevant molecules using high intensity, tuneable, infrared light from FEL-2 at FELIX. Irradiated ices consisted of CO or N2 mixed with amorphous H2O ice, adsorbed on a cryogenically cooled (9 K) metallic substrate surface. Isotope effects were also investigated using 13CO and D2O in place of the 12CO and H2O ice. Ices were irradiated with light in the mid-IR range from 2.8 – 16 µm, at wavelengths corresponding to the vibrational modes of the H2O/D2O and 12CO/13CO or N2 vibrational modes. Changes in the ices were monitored using a combination of pre- and post-irradiation reflection absorption infrared spectroscopy to monitor changes in the ice morphology, and photon induced desorption using a quadrupole mass spectrometer, to measure desorption during irradiation.
Studies show that CO and N2 desorb from the mixed ices, following irradiation at wavelengths corresponding to the H2O/D2O vibrational modes. These results show that a number of different desorption channels exist on these icy surfaces, and also demonstrate that infrared induced desorption should be included in astrophysical models of ices on dust grain surfaces.
