Photodestruction of Relevant Interstellar Molecules in Ice Mixtures

Abstract

UV photodestruction of some interstellar molecules is studied in different kinds of ices. CH 4 , CH 3 OH, NH 3 , CO 2 , CO, and HNCO are photolyzed as pure ices, or mixed with water or molecular nitrogen, at about 10 K. The destruction cross sections of these molecules are estimated for use in photochemical models of interstellar ices. We show that the destruction rate depends on the ice in which the studied compound is embedded.

Chemical Evolution of a Co Ice Induced by Soft X-Rays

“…Laboratory studies of the evolution of interstellar ice analogs under the effect of photon irradiation and ionized particles have greatly contributed to our understanding of the chemistry of complex organic molecules synthesized in space. In particular, the chemical modifications of CO ices, both pure or in mixture, have been studied under the effect of vacuum (Gerakines et al 1996;Gerakines & Moore 2001;Cottin et al 2003;Loeffler et al 2005;Chen et al 2014) and extreme-ultraviolet radiation (Wu et al 2005), ions (Gerakines & Moore 2001;Trottier & Brooks 2004;Loeffler et al 2005;Domaracka et al 2010) and electrons (Jamieson et al 2006). Muñoz Caro et al (2010) measured the photodesorption yield of CO ice under ultraviolet irradiation, finding the release yield at 15 K to be about one order of magnitude higher than previous estimates.…”

Controlling the emission profile of an H2discharge lamp to simulate interstellar radiation fields

“…For the last two decades, microwave discharge hydrogen-flow lamps (MDHLs;Warneck 1962;Davis & Braun 1968) have been widely used as vacuum-ultraviolet (VUV) light sources in laboratory experiments to simulate interstellar radiation fields in astrochemical studies (Westley et al 1995;Gerakines et al 1996;Baratta et al 2002;Muñoz Caro et al 2002, 2010Cottin et al 2003;Leto & Baratta 2003;Loeffler et al 2005;Watanabe et al 2007;Öberg et al 2007;Islam et al 2014;Cook et al 2014;Henderson & Gudipati 2015). These experiments aim to simulate and ultimately unravel the complex photoprocesses (photodesorption, photodissociation, and photochemistry) taking place in interstellar ice analogues.…”

“…the dependence on the experimental settings, influence both the total photon flux and the SED of the impacting radiation at the ice sample. In other situations the flux of the lamp is either directly measured using a National Institute of Standards and Technology (NIST) calibrated photodiode or indirectly by actinometry using for example the conversion of O 2 to O 3 (Gerakines et al 1996;Cottin et al 2003;Islam et al 2014;Fulvio et al 2014). When using a NIST calibrated photodiode for photon flux measurements, the quantum yield is known at different wavelengths.…”

“…In the actinometry case, the O 2 to O 3 conversion efficiency typically used is taken from gas phase experiments performed by Groth (1937). Recent experiments indicate that the quantum efficiency in the solid state is significantly lower (Cottin et al 2003;Fulvio et al 2014) and hint toward a wavelength dependency, although detailed wavelength dependent studies are still lacking in the literature. It is clear that both calibration methods require knowledge of the emission spectrum of the lamp to accurately determine the flux at different photon energies, which strongly depends on the experimental settings.…”

Space as a Tool for Astrobiology: Review and Recommendations for Experimentations in Earth Orbit and Beyond

“…about 50 times more intense than from the Sun. Thus, 6 days of exposure at SOLEIL can generate Thuillier et al 2004a, upper left) and typical laboratory VUV lamps (H 2 ) (from Cottin et al 2003-lamp 1, upper right, from Chen et al 2014-lamp 2, middle left and Es-sebbar et al 2015. To date, no laboratory lamp is able to accurately simulate the solar spectrum in the VUV, although the most recent developments are much improved and have eliminated the strong emission at 160 nm by adding He to H 2 .…”