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The chemistry of multiply deuterated molecules in protoplanetary disks : I. the outer disk

Show simple item record Willacy, K. 2008-10-21T20:48:24Z 2008-10-21T20:48:24Z 2007-05-01
dc.identifier.citation The Astrophysical Journal, 660:441-460, 2007 May 1 en_US
dc.identifier.clearanceno 06-0685
dc.description.abstract We present new models of the deuterium chemistry in protoplanetary disks, including, for the first time, multiply deuterated species. We use these models to explore whether observations in combination with models can give us clues as to which desorption processes occur in disks.We find, in common with other authors, that photodesorption can allow strongly bound molecules such as HDO to exist in the gas phase in a layer above the midplane. Models including this process give the best agreement with the observations. In the midplane, cosmic-ray heating can desorb weakly bound molecules such as CO and N2. We find the observations suggest that N2 is gaseous in this region, but that CO must be retained on the grains to account for the observed DCO+/HCO+. This could be achieved by CO having a higher binding energy than N2 (as may be the case when these molecules are accreted onto water ice) or by a smaller cosmic-ray desorption rate for CO than assumed here, as suggested by recent theoretical work. For gaseous molecules the calculated deuteration can be greatly changed by chemical processing in the disk from the input molecular cloud values. On the grains singly deuterated species tend to retain the D/H ratio set in the molecular cloud, whereas multiply deuterated species are more affected by the disk chemistry. Consequently, the D/H ratios observed in comets may be partly set in the parent cloud and partly in the disk, depending on the molecule. en_US
dc.description.sponsorship NASA/JPL en_US
dc.language.iso en_US en_US
dc.publisher The American Astronomical Society. en_US
dc.subject circumstellar matter en_US
dc.subject molecules en_US
dc.subject star formation en_US
dc.subject deuterium chemistry
dc.title The chemistry of multiply deuterated molecules in protoplanetary disks : I. the outer disk en_US
dc.type Article en_US

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