Isotopologues Detection and Quantitative Analysis by Mid‐Infrared Dual‐Comb Laser Spectroscopy

Abstract

Isotopologues are molecules that differ from the parent molecule only in their isotopic composition. For example, ordinary light water (H 2 O), semi‐heavy water (HDO), and heavy water (D 2 O) are isotopologues of the same molecule. They have the same chemical formula and bonding arrangement of atoms, but at least one atom has a different number of neutrons than the parent. Isotopologues that differ only by the location of an isotopically modified element are called isotopomers. For example, the 15 N isotope in the N 2 O molecule can be either next to the oxygen atom or second next to it; thus, N 15 NO and 15 NNO are isotopomers of the same molecule. Detecting isotopologues of different molecules is critical in such fields as astrobiology, biogeochemistry, personalized medicine, and forensics, with mass spectrometry being a major technique to distinguish between different isotopologues. In this article, I focus on a new technique for detection of isotopologues based on laser spectroscopy. The backbone of this technology is massively parallel spectroscopic probing in the mid‐infrared spectral region by a frequency comb – a broad spectrum composed of some million phase‐locked equidistant sharp spectral lines – produced by a subharmonic optical parametric oscillator (OPO). Through assessing their unique rotational‐vibrational absorption signatures, we are able to simultaneously detect numerous molecules and their isotopologues in a mixture of gases, in real time and with one part‐per‐billion detection capability.

Open-path measurement of stable water isotopologues using mid-infrared dual-comb spectroscopy

“…This technique achieves high spectral resolution (here, the spectral point spacing is 200 MHz or 0.0067 cm -1 ) with no instrument lineshape while also spanning hundreds of wavenumbers . Several demonstrations have already shown the potential of laboratory DCS for isotopologue measurements (Muraviev et al, 2018;Vodopyanov, 2020;Parriaux et al, 2022). Open-path DCS optical paths can be easily reconfigured using remotely controlled telescopes to adjust to measurement conditions (Coburn et al, 2018) and can be spatially scanned using mobile reflectors (Cossel et al, 2017), which could enable better tomographic characterization of evaporation and transpiration in agricultural systems and natural ecosystems (Welp et al, 2008).…”

Open-path measurement of stable water isotopologues using mid-infrared dual-comb spectroscopy

“…This technique achieves high spectral resolution (here, the spectral point spacing is 200MHz or 0.0067cm −1 ) with no instrument line shape while also spanning hundreds of wavenumbers ( Waxman et al, 2017 ). Several demonstrations have already shown the potential of laboratory DCS for isotopologue measurements ( Muraviev et al, 2018 ; Vodopyanov, 2020 ; Parriaux et al, 2022 ). Open-path DCS optical paths can be easily reconfigured using remotely controlled telescopes to adjust to measurement conditions ( Coburn et al, 2018 ) and can be spatially scanned using mobile reflectors ( Cossel et al, 2017 ), which could enable better tomographic characterization of evaporation and transpiration in agricultural systems and natural ecosystems ( Welp et al, 2008 ).…”

Isotope Ratio Dual-Comb Spectrometer

“…DCS shows several characteristics such as a high spectral resolution, no mobile parts in the setup, and the potential to perform real-time analyses. These features are very interesting for IRMs in gases, and to the best of our knowledge, only a few works have considered the use of DCS for this application [23,24], but no quantitative measurements were performed.…”