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Title: Rapid and sensitive quantification of isotopic mixtures using a rapidly-swept external cavity quantum cascade laser

A rapidly-swept external-cavity quantum cascade laser with an open-path Herriott cell is used to quantify gas-phase chemical mixtures of D2O and HDO at a rate of 40 Hz (25-ms measurement time). The chemical mixtures were generated by evaporating D2O liquid near the open-path Herriott cell, allowing the H/D exchange reaction with ambient H2O to produce HDO. Fluctuations in the ratio of D2O and HDO on timescales of <1 s due to the combined effects of plume transport and the H/D exchange chemical reaction are observed. Noise-equivalent concentrations (1σ) (NEC) of 147.0 ppbv and 151.6 ppbv in a 25-ms measurement time are determined for D2O and HDO, respectively, with a 127-m optical path. These NECs are improved to 23.0 and 24.0 ppbv with a 1-s averaging time for D2O and HDO, respectively. NECs <200 ppbv are also estimated for N2O, 1,1,1,2–tetrafluoroethane (F134A), CH4, acetone and SO2 for a 25-ms measurement time. Finally, the isotopic precision for measurement of the [D2O]/[HDO] concentration ratio of 33‰ and 5‰ is calculated for the current experimental conditions for measurement times of 25 ms and 1 s, respectively.
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  1. Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Optical Sensing
Publication Date:
Report Number(s):
Journal ID: ISSN 2304-6732; PII: photonics3020033
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Additional Journal Information:
Journal Volume: 3; Journal Issue: 2; Journal ID: ISSN 2304-6732
Research Org:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org:
USDOE National Nuclear Security Administration (NNSA), Office of Nonproliferation and Verification Research and Development (NA-22)
Country of Publication:
United States
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; external cavity quantum cascade laser; infrared spectroscopy; trace-gas sensing
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