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Computational Confirmation of the Carrier for the "XCN" Interstellar Ice Bank: OCN(-) Charge Transfer ComplexesRecent experimental studies provide evidence that carrier for the so-called XCN feature at 2165 cm(exp -1) (4.62 micron) in young stellar objects is an OCN(-)/NH4(+) charge transfer (CT) complex that forms in energetically processed interstellar icy grain mantles. Although other RCN nitriles and RCN iosonitriles have been considered, Greenberg's conjecture that OCN(-) is associated with the XCN feature has persisted for over 15 years. In this work we report a computational investigation that thoroughly confirms the hypothesis that the XCN feature observed in laboratory studies can result from OCN(-)/NH4(+) CT complexes arising from HNCO and NH3, in a water ice environment. Density functional theory calculations with theory calculations with HNCO, NH3, and up to 12 waters reproduce seven spectroscopic measurements associated with XCN: the band origin of the asymmetric stretching mode of OCN(-), shifts due to isotopic substitutions of C, N, O, and H, and two weak features. However, very similar values are also found for the OCN(-)/NH4(+) CT complex arising from HOCN and NH3. In both cases, the complex forms by barrierless proton transfer from HNCO or HOCN to NH3 during the optimization of the solvated system. Scaled B3LYP/6-31+G** harmonic frequencies for HNCO and HOCN cases are 2181 and 2202 cm(exp -1), respectively.
Document ID
20070025476
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Park, J.-Y.
(Molecular Research Inst. CA, United States)
Woon, D. E.
(Molecular Research Inst. CA, United States)
Date Acquired
August 23, 2013
Publication Date
August 1, 2004
Publication Information
Publication: Astrophysics Journal
Volume: 601
Subject Category
Astrophysics
Funding Number(s)
CONTRACT_GRANT: NAG5-13482
Distribution Limits
Public
Copyright
Other

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