Paper SS1-ThA7
Surface Science Investigations of Photoprocesses in Model Interstellar Ices

Thursday, October 18, 2007, 4:00 pm, Room 608

In the last decade or so, the astronomy and astrophysics communities have come to realise that physical and chemical processes occurring at the surfaces of interstellar dust grains play a key role in the chemical evolution of the Universe. Grain surfaces promote the formation of molecular hydrogen and simple hydride species such as water, ammonia and methane. As such, at the temperatures found in the most chemically rich regions of the interstellar medium (ISM), typically 20 K or less, they reactively accrete icy mantles containing these species. Condensation of molecules from the gaseous ISM occurs in parallel, producing water-rich icy mantles that are readily observed in the infrared in many lines of sight towards star-forming regions. These mantles play a crucial role as reservoirs for small molecular coolants during the earliest phases of star formation, promoting the formation of small, long-lived stars such as our own Sun. They also act as chemical nanofactories driven by energy from photons and cosmic rays to produce increasingly complex chemical species from simple ice mixtures, hence seeding the Universe with a complex chemical soup. While numerous studies exist in the literature seeking to understand the chemical evolution of water-rich icy mixtures during irradiation by light and charged particles, the majority of these high vacuum studies have failed to address the fundamental question of the disposition of the incident energy. How much of the photon or charged particle's energy goes into driving physical processes (morphological change, desorption, etc.) as opposed to driving chemical processes? Here we will report on recent surface science investigations aimed at addressing this most fundamental of questions in laboratory astrochemistry.