A NEW DETERMINATION OF THE BINDING ENERGY OF ATOMIC OXYGEN ON DUST GRAIN SURFACES: EXPERIMENTAL RESULTS AND SIMULATIONS

• Published in: The Astrophysical journal Vol. 801; no. 2; pp. 1 - 7
• Main Authors: He, Jiao, Shi, Jianming, Hopkins, Tyler, Vidali, Gianfranco, Kaufman, Michael J.
• Format: Journal Article
• Language: English
• Published: United States The American Astronomical Society 10.03.2015
• Subjects: Astrochemistry; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; Atomic oxygen; ATOMS; BINDING ENERGY; CHEMISTRY; CLOUDS; COSMIC DUST; DESORPTION; Dust; Dust control; dust, extinction; FAR ULTRAVIOLET RADIATION; Grains; ICE; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; INTERSTELLAR GRAINS; INTERSTELLAR SPACE; ISM: abundances; ISM: atoms; ISM: molecules; Mathematical models; MOLECULES; OXYGEN; POROUS MATERIALS; SILICATES; SURFACES; WATER
• ISSN: 0004-637X; 1538-4357; 1538-4357
• DOI: 10.1088/0004-637X/801/2/120

ABSTRACT The energy to desorb atomic oxygen from an interstellar dust grain surface, Edes, is an important controlling parameter in gas-grain models; its value impacts the temperature range over which oxygen resides on a dust grain. However, no prior measurement has been done of the desorption energy. We report the first direct measurement of Edes for atomic oxygen from dust grain analogs. The values of Edes are 1660 60 and 1850 90 K for porous amorphous water ice and for a bare amorphous silicate film, respectively, or about twice the value previously adopted in simulations of the chemical evolution of a cloud. We use the new values to study oxygen chemistry as a function of depth in a molecular cloud. For n = 104 cm−3 and G0 = 102 (G0 = 1 is the average local interstellar radiation field), the main result of the adoption of the higher oxygen binding energy is that H2O can form on grains at lower visual extinction AV, closer to the cloud surface. A higher binding energy of O results in more formation of OH and H2O on grains, which are subsequently desorbed by far-ultraviolet radiation, with consequences for gas-phase chemistry. For higher values of n and G0, the higher binding energy can lead to a large increase in the column of H2O but a decrease in the column of O2.