Vacuum Ultra-Violet Spectroscopy of Laboratory-Simulated Astrophysical Ices
Abstract
Over recent years it has become clear that solid phase processes in the interstellar medium (ISM) are responsible for a significant amount of molecular formation in these regions. A combination of astronomical spectroscopy and laboratory-based simulations has greatly enhanced our understanding of those molecules which are present in the ISM and provided information on their formation mechanisms. Although infra-red spectroscopy has been widely used in these studies and is a common observational tool other spectroscopic techniques are now being developed. We have carried out a number of experiments looking at the electronic structure of simple molecular ices (such as H2O, NH3, CO, CO2, SO2 and CH4) using vacuum ultra-violet (VUV) spectroscopy. In addition to complementing existing infra-red spectra, knowing the electronic structure of ices allows us to understand the processes which take place during irradiation by ultra-violet photons, a common source of ice surface modification in the interstellar medium. In our experiments we have used synchrotron beam-lines at Daresbury Laboratory (UK) and Aarhus University (Denmark) as the irradiating source providing UV light at wavelengths between 120nm and 350nm. A small ultra-high vacuum chamber with an in-built cryostat system was attached to the beam-line (for more information see Dawes, Holtom & Mason (2003)). A magnesium fluoride or calcium fluoride substrate was cooled to between 20K and 100K allowing the sample molecules to physisorb upon it. Typical ice thicknesses range from 0.1μm and 3μm, depending on the UV absorption properties of the ice involved. In this poster we present VUV spectra of several typical astrochemical molecules showing how the electronic structures of different ice systems are affected by their temperature and deposition speed. The importance of VUV spectroscopy as an astrochemical and possible observation technique will be discussed at the meeting.
- Publication:
-
Astrochemistry: Recent Successes and Current Challenges
- Pub Date:
- 2005
- Bibcode:
- 2005IAUS..231P.128D
- Keywords:
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- astrochemistry;
- ISM: molecules;
- planets and satellites: general;
- techniques: spectroscopic;
- ultraviolet: ISM