Direct, Precise Measurements of Isotopologue Abundance Ratios in CO₂ Using Molecular Absorption Spectroscopy: Application to δ ¹⁷O

We present an ultrasensitive absorption spectrometer based on a 30 Hz/s stability, sub-kHz line width laser source coupled to a high-stability cavity-ring-down-spectroscopy setup. It provides direct and precise measurements of the isotopic ratios δ ¹⁷O and δ ¹⁸O in CO₂. We demonstrate the first optical absorption measurements of ¹⁷O anomalies in CO₂ with a precision better than 10 ppm, matching the requirements for paleo-environmental applications. This illustrates how optical absorption methods have become a competitive alternative to state-of-the-art isotopic ratio mass spectrometry techniques. (authors)