Laboratory Evidence for Efficient Water Formation in Interstellar Ices

Even though water is the main constituent in interstellar icy mantles, its chemical origin is not well understood. Three different formation routes have been proposed following hydrogenation of O, O2, or O3 on icy grains, but experimental evidence is largely lacking. We present a solid state astrochemical laboratory study in which one of these routes is tested. For this purpose O2 ice is bombarded by H or D atoms under ultrahigh vacuum conditions at astronomically relevant temperatures ranging from 12 to 28 K. The use of reflection absorption infrared spectroscopy (RAIRS) permits derivation of reaction rates and shows efficient formation of H2O (D2O) with a rate that is surprisingly independent of temperature. This formation route converts O2 into H2O via H2O2 and is found to be orders of magnitude more efficient than previously assumed. It should therefore be considered as an important channel for interstellar water ice formation as illustrated by astrochemical model calculations.

[1]  A. Kouchi,et al.  Formation of hydrogen peroxide and water from the reaction of cold hydrogen atoms with solid oxygen at 10 K , 2008, 0805.0055.

[2]  E. F. Dishoeck,et al.  Hydrogen adsorption and diffusion on amorphous solid water ice , 2007 .

[3]  N. Mason,et al.  Temperature-dependent Formation of Ozone in Solid Oxygen by 5 keV Electron Irradiation and Implications for Solar System Ices , 2007 .

[4]  E. Herbst,et al.  Simulation of the Formation and Morphology of Ice Mantles on Interstellar Grains , 2007, 0707.2744.

[5]  S. Schlemmer,et al.  Photodesorption of CO Ice , 2007, 0705.0260.

[6]  E. F. Dishoeck,et al.  Desorption of CO and O2 interstellar ice analogs , 2007, astro-ph/0702322.

[7]  A. Kouchi,et al.  Dependence of the effective rate constants for the hydrogenation of CO on the temperature and composition of the surface , 2006 .

[8]  R. Carlson,et al.  Synthesis of hydrogen peroxide in water ice by ion irradiation , 2006 .

[9]  R. Kaiser,et al.  Laboratory Studies on the Formation of Ozone (O3) on Icy Satellites and on Interstellar and Cometary Ices , 2005 .

[10]  Yuka Kimura,et al.  New Rate Constants of Hydrogenation of CO on H2O-CO Ice Surfaces , 2005 .

[11]  J. Lemaire,et al.  Isotopic segregation of molecular hydrogen on water ice surface at low temperature , 2005 .

[12]  O. Biham,et al.  Molecular Hydrogen Formation on Ice Under Interstellar Conditions , 2004, astro-ph/0412202.

[13]  E. Dartois,et al.  Mapping ices in protostellar environments on 1000 AU scales - Methanol-rich ice in the envelope of Serpens SMM 4 , 2004, astro-ph/0407316.

[14]  A. Tielens,et al.  Interstellar Ice: The Infrared Space Observatory Legacy , 2004 .

[15]  R. Kaiser,et al.  Untangling the formation of the cyclic carbon trioxide isomer in low temperature carbon dioxide ices , 2004 .

[16]  A. Luntz,et al.  Importance of Surface Morphology in Interstellar H2 Formation , 2003, Science.

[17]  A. Kouchi,et al.  The Dependence of H2CO and CH3OH Formation on the Temperature and Thickness of H2O-CO Ice during the Successive Hydrogenation of CO , 2003 .

[18]  E. Herbst,et al.  New models of interstellar gas–grain chemistry – I. Surface diffusion rates , 2002 .

[19]  K. Tschersich.  Intensity of a source of atomic hydrogen based on a hot capillary , 2000 .

[20]  K. G. Tschersich,et al.  Formation of an atomic hydrogen beam by a hot capillary , 1998 .

[21]  K. Hiraoka,et al.  Gas-Grain Processes for the Formation of CH4 and H2O: Reactions of H Atoms with C, O, and CO in the Solid Phase at 12 K , 1998 .

[22]  T. Prusti,et al.  Detection of Abundant CO2 Ice in the Quiescent Dark Cloud Medium toward Elias 16 , 1998 .

[23]  E. Herbst,et al.  Three-phase chemical models of dense interstellar clouds: gas, dust particle mantles and dust particle surfaces , 1993 .

[24]  A. Tielens,et al.  Interstellar solid CO: polar and nonpolar interstellar ices. , 1991, The Astrophysical journal.

[25]  J. Walraven,et al.  Helium‐temperature beam source of atomic hydrogen , 1982 .

[26]  F. Gillett,et al.  SPECTRA OF THE BECKLIN--NEUGEBAUER POINT SOURCE AND THE KLEINMANN--LOW NEBULA FROM 2.8 TO 13.5 MICRONS. , 1973 .