Quantum cascade laser absorption spectrometer with a low temperature multipass cell for precision clumped CO₂...

Area of Science:

• Spectroscopy
• Analytical Chemistry
• Physical Chemistry

Background:

• Isotopic analysis of carbon dioxide (CO2) is crucial for understanding chemical kinetics and geological processes.
• Traditional methods face challenges with precision, especially when dealing with interfering hot-band transitions.

Purpose of the Study:

• To develop a highly precise quantum cascade laser-based absorption spectrometer for analyzing CO2 isotopologues.
• To investigate the kinetic isotope exchange reaction involving 12CO2, 12C18O2, and 12C16O18O.
• To determine the temperature dependence of the equilibrium constant for this reaction.

Main Methods:

• Utilized a compact segmented circular multipass cell (SC-MPC) with a 6 m optical path length.
• Integrated the SC-MPC with an effective cooling system for operation at cryogenic temperatures (153 K for CO2).
• Employed quantum cascade laser (QCL) absorption spectroscopy for high-resolution measurements.

Main Results:

• Achieved high precision (0.05‰) in measuring ratios of CO2 isotopologues ([12C18O2]/[12C16O2] and [12C16O18O]/[12C16O2]) within 25 s integration time.
• Successfully suppressed interfering hot-band transitions by operating at cryogenic temperatures.
• Determined the variation of the equilibrium constant (K) for the specified CO2 isotope exchange reaction at 300 K and 1273 K.

Conclusions:

• The developed QCL spectrometer with a cryogenically cooled SC-MPC offers enhanced analytical precision for CO2 isotopologue analysis.
• This technique is effective for studying kinetic isotope exchange reactions and determining thermodynamic parameters.
• The findings contribute to a better understanding of CO2 isotope fractionation mechanisms.