Computational confirmation of the carrier for the "XCN" interstellar ice band: OCN- charge transfer complexes

Jin Young Park, David E. Woon

Research output: Contribution to journalArticlepeer-review

Abstract

Recent experimental studies provide evidence that the carrier for the so-called XCN feature at 2165 cm-1 (4.62 μm) 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 RNC isonitriles 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-/NH 4+ CT complexes arising from HNCO and NH3 in a water ice environment. Density functional theory calculations with HNCO, NH 3, 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 NH 3. 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 the HNCO and HOCN cases are 2181 and 2202 cm-1, respectively.

Original languageEnglish (US)
Pages (from-to)L63-L66
JournalAstrophysical Journal
Volume601
Issue number1 II
DOIs
StatePublished - Jan 20 2004
Externally publishedYes

Keywords

  • Astrochemistry
  • ISM: lines and bands
  • Infrared: ISM

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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