Carbonaceous Nanoparticles Molecular Factories in the Interstellar Medium

by Ralf Kaiser (UHM - Dept of Chemistry, W.M. Keck Research Laboratory for Astrochemistry)

Thursday Oct 31, 2013, 3:30 PM → 4:30 PM Pacific/Honolulu

During the last decade, carbonaceous nanostructures have received considerable attention from the astronomy and laboratory astrophysics communities as they are contemplated to catalyze the cosmic-ray induced formation of astrobiologically relevant molecules such as sugars, amino acids, and even dipeptides in the interstellar medium (ISM). The underlying formation routes of these molecules have remained inconclusive to date and cannot be explained by classical networks of gas phase ion-molecule reactions with modeled abundances toward star forming regions such as Sgr B2 being up to three orders of magnitude less than the actual observations. Therefore, a key source providing these molecules is missing. Subsequent models attempted to boost the production rates by incorporating grain-surface processes on interstellar grains at temperatures as low as 10 K. But these models also failed to explain the observed abundances. The inadequate agreement between modeled and observed abundances is based on the fact that current models disregard the non-equilibrium processing of the ‘bulk’ ice mantle on interstellar grains with thicknesses up to a few 100 nm by ionizing radiation such as galactic cosmic rays and the vacuum ultraviolet photon field even present deep inside molecular clouds such as TMC-1. However, these processes have been rarely investigated under well-defined laboratory conditions reproducing interstellar environments. This talk compiles recent accomplishments on the elucidation of the formation of astrobiologically important molecules on ice coated interstellar carbonaceous nanoparticles (interstellar grains) by ionizing radiation. These studies utilize novel detection techniques in the condensed phase (cold molecular clouds) and also upon sublimation of the ices into the gas phase (hot core stage) exploiting reflectron time of mass spectroscopy coupled to single photon photoionization (ReTOF-PI) as generated via resonant four wavemixing in pulsed noble gas jets. We also shed light on the actual formation of key intermediates – polycyclic aromatic hydrocarbons (PAHs) – leading eventually to the formation of carbonaceous nanostructures even in cold molecular clouds. Our studies present for the very first time a comprehensive investigation of the underlying processes leading to the formation of complex, bio-relevant molecules in the interstellar medium in the condensed phase, which can in turn be exploited to predict the existence of hitherto unobserved molecules in the interstellar medium to be searched for by the Atacama Large Millimeter/submillimeter Array (ALMA).
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