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Precise Measurements of 12CH2D2 by Tunable Infrared Laser Direct Absorption Spectroscopy

Research output: Contribution to journalArticle (Academic Journal)

  • Yenny Gonzalez
  • David D. Nelson
  • Joanne H. Shorter
  • J. Barry McManus
  • Christoph Dyroff
  • Michael Formolo
  • David T. Wang
  • Colin M. Western
  • Shuhei Ono
Original languageEnglish
Article number23
Pages (from-to)14967-14974
Number of pages8
JournalAnalytical Chemistry
DateAccepted/In press - 30 Oct 2019
DatePublished (current) - 30 Oct 2019


We present precise measurements of doubly deuterated methane (12CH2D2) in natural methane samples using tunable infrared laser direct absorption spectroscopy (TILDAS). Using a 413 m optical path length astigmatic Herriott cell and two quantum cascade lasers (QCLs) scanning the spectral regions of 1090.46 ± 0.1 and 1200.23 ± 0.1 cm-1, the instrument simultaneously measures the five main isotopologues of methane. The ratios 13CH3D/12CH4 and 12CH2D2/12CH4 are measured at 0.01‰ and 0.5‰ (1σ) instrumental precision, respectively. The instrumental accuracy was assessed by measuring a series of methane gases with a range of δ13C and δD values but with the abundances of all isotopologues driven to thermal equilibrium at 250 °C. The estimated accuracy of Δ12CH2D2 is 1‰ (1σ) on the basis of the results of the heated methane samples. This new TILDAS instrument provides a simple and rapid technique to explore the sources of methane in the environment.



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