Millimeter and submillimeter rest frequencies for NaCN (X̃ 1A′): A remarkably abundant circumstellar molecule

D. T. Halfen, L. M. Ziurys

Research output: Contribution to journalArticlepeer-review

7 Scopus citations

Abstract

The pure rotational spectrum of NaCN has been recorded in the millimeter/submillimeter region using direct absorption techniques, the first experimental study of this molecule at frequencies above 40GHz. The species was produced in the gas phase in an AC discharge by the reaction of sodium vapor with cyanogen. Twelve rotational transitions of NaCN have been measured in the range of 180-530GHz, extending the previous microwave data to millimeter/submillimeter frequencies. Multiple Ka asymmetry components were recorded in each rotational transition up to Ka = 5 or 6, a total of 131 individual lines. These data have been analyzed with a standard asymmetric top Hamiltonian, combined with prior microwave measurements. Higher-order centrifugal distortion terms were clearly needed to model the millimeter-wave transitions of this floppy molecule. From this revised set of spectroscopic constants, accurate frequency predictions can now be made up to 600GHz for NaCN for the lower-value Ka components (Ka ≤ 4). Based on the new laboratory data and past spectral surveys, a revised abundance for NaCN in IRC+10216 has been estimated. For a 5″ source, the fractional abundance for this molecule was found to be f (NaCN/H2) 1× 10-8, comparable to that of c-C3H2. These new frequency measurements should aid in line identification in surveys in the 0.8 mm band and at shorter wavelengths.

Original languageEnglish (US)
Article number107
JournalAstrophysical Journal
Volume730
Issue number2
DOIs
StatePublished - Apr 1 2011

Keywords

  • ISM: molecules
  • astrochemistry
  • line: identification
  • methods: laboratory
  • molecular data
  • stars: AGB and post-AGB

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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