Methane Clumped Isotopologue Detection Using Cavity-ring-down Spectroscopy

Methane (CH₄) is a potent greenhouse gas, making its source attribution critical for climate change mitigation. Traditional measurement techniques often struggle with mixed sources; however, clumped isotope analysis can achieve better source differentiation. In this work, detection of clumped methane isotopologues has been demonstrated using cavity-ringdown spectroscopy (CRDS). The technique employs a tunable quantum cascade laser coupled into a highly reflective optical cavity. The ring-down time differences are then measured to determine abundances of isotopologues. Measurements were performed using industrial-grade methane, focusing on the spectral region from 2228.4 to 2229.2 cm-1. The recorded spectra demonstrate CRDS as an effective method for measuring clumped methane isotopologues, addressing absorption lines assigned in the recently published FTIR spectra [1].