UV induced Chemistry of Polycyclic Aromatic Hydrocarbons in NH_3-containing Interstellar Ice Analogues
Abstract
Polycyclic Aromatic Hydrocarbons are expected to be widely present in the interstellar medium. For the typical temperatures in space, they will freeze out on icy dust grains, like other species, such as water and ammonia. Optical spectra of PAHs in water ice have become available recently using a new setup at Leiden (OASIS - Optical Absorption Setup for Ice Spectroscopy). This setup allows to study the time resolved PAH and PAH photoproduct behavior upon hard UV photolysis, evidencing an active PAH chemistry in the ice for temperatures in the 15-150 K regime. The matrix surrounding turns out to be very important. As an extension of the previous PAH:H2O ices, here the first results are presented for UV irradiated PAH:NH3 and PAH:NH3/H2O ices. In this way PAH destruction and molecule formation can be monitored in situ and on line. It is found that whereas H2O ices particularly result in the formation of PAH-cations, ammonia seems to favor the formation of anions in the ice. After photolysis is stopped, the PAH anion signal vanishes. At this stage these results are interpreted by assuming that charged species form in interstellar ice by electron transfer from ammonia photoproducts, rather than acid-base proton transfer.
- Publication:
-
The Molecular Universe
- Pub Date:
- May 2011
- Bibcode:
- 2011IAUS..280P.144C