Room-temperature Quantification Of 14co2 Below The Natural Abundance With Two-color, Cavity Ringdown Spectroscopy

Jiang, Jun

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https://hdl.handle.net/2142/116609 Copy

Description

Title

Room-temperature Quantification Of 14co2 Below The Natural Abundance With Two-color, Cavity Ringdown Spectroscopy

Author(s)

Jiang, Jun

Contributor(s)

McCartt, A. Daniel

Issue Date

2022-06-23

Keyword(s)

Instrument/Technique Demonstration

Abstract

In this talk, we report the first room-temperature optical detection of radiocarbon dioxide ($^{14}$CO$_2$) samples at concentrations below the natural abundance level (1.2 parts per trillion, $^{14}$C/C), using the recently-developed two-color, mid-IR, pump-probe, cavity ringdown (CRD) technique. With 3 minutes of averaging, our two-color CRD method successfully differentiates, with an accuracy of 8$\%$ of the $^{14}$C natural abundance, five combusted $^{14}$C standards with $^{14}$CO$_2$ concentrations ranging from petrogenic (zero $^{14}$C/C) to approximately double the contemporary abundance. Room-temperature quantification of $^{14}$CO$_2$ is not possible with any existing one-photon cavity-enhanced techniques at our demonstrated $^{14}$C concentration levels, due to severe spectral overlap between the very weak target $^{14}$CO$_2$ $\nu_3$-band transitions ($\sim$5/s ringdown rate at natural abundance) and the strong hot-band transitions of CO$_2$ isotopologues ($>$10000/s). All previous CRD-based, one-photon $^{14}$CO$_2$ measurements at the sub-natural-abundance level required cooling of the test gas (-20 to -100$^{\circ}$C) to mitigate the strong background absorption. Our unprecedented high-sensitivity, high-selectivity detection of $^{14}$CO$_2$ at room temperature is made possible by the dual-background compensation capabilities of the two-color CRD technique. The two-color measurement utilizes two cavity-enhanced pump and probe lasers to excite, respectively, the $\nu_3=1$$\leftarrow$0, P(14) and $\nu_3=2$$\leftarrow$1, R(13) rovibrational transitions of $^{14}$CO$_2$. With the pump radiation switched off during every other probe ringdown events ($>$2 kHz rate), the CRD rate fluctuations and strong one-photon absorption interference are effectively cancelled out during the two-color measurements. Highly-selective, room-temperature detection of weak $^{14}$CO$_2$ absorption signals reduces the technical and operational burdens for cavity-enhanced measurements of radiocarbon. This is a crucial achievement that will enable laser-based radiocarbon quantification outside a laser laboratory setting, and benefit a wide range of scientific applications, such as $^{14}$C-labeling analysis of biomedical samples and field monitoring of fossil fuel emission.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

eng

Handle URL

https://hdl.handle.net/2142/116609

DOI

https://doi.org/10.15278/isms.2022.RJ03

Copyright and License Information

Copyright 2022 held by the authors

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