Experimental evidence for water formation on interstellar dust grains by hydrogen and oxygen atoms

摘要

Context. The synthesis of water is one necessary step in theorigin and development of life. It is believed that pristine water isformed and grows on the surface of icy dust grains in dark interstellarclouds. Until now, there has been no experimental evidence whether thisscenario is feasible or not on an astrophysically relevant template andby hydrogen and oxygen atom reactions. Aims. We present here the first experimental evidence of watersynthesis by such a process on a realistic analogue of grain surface indense clouds, i.e., amorphous water ice. Methods. Atomic beams of oxygen and deuterium are aimed at a porous water ice substrate (H2O) held at 10K. Products are analyzed by the temperature-programmed desorption technique. Results. We observe the production of HDO and D2O,indicating that water is formed under conditions of the denseinterstellar medium from hydrogen and oxygen atoms. This experimentopens up the field of a little explored complex chemistry that couldoccur on dust grains,which is believed to be the site where keyprocesses lead to the molecular diversity and complexity observed inthe Universe. Key words: astrochemistry - ISM: molecules - dust, extinction- methods: laboratory - molecular processes