Measurements doubly-substituted methane isotopologue (13CH3D and 12CH2D2) abudance using frequency stabilized mid-ir cavity ringdown spectroscopy

In this work, we demonstrated a spectroscopic method of measuring abundances of doubly-substituted methane isotopologues ($^{13}$CH$_{3}$D, $^{12}$CH$_2$D${2}$). In this method, we use a frequency stabilized cavity ringdown spectroscopy (FS-CRDS) technique to measure $\Delta$$^{12}$CH$_2$D${2}$ in naturally abundant methane to sub 0.1$\%$ level within one hour of average. Compare to traditional isotope-ratio mass spectrometer, which requires more than 24 hours of average to achieve comparable precision, this method provides a fast way of measuring clumped isotopologue abundance optically without destroying samples