Oxygen isotope ratio measurements in CO_2 by means of a continuous-wave quantum cascade laser at 4.3 μm (original) (raw)

A mid-infrared laser spectrometer was developed for simultaneous high-precision 18 O/ 16 O and 17 O/ 16 O isotope ratio measurements in carbon dioxide. A continuous-wave, liquid-nitrogen cooled, distributed feedback quantum cascade laser, working at a wavelength of 4.3 m, was used to probe 12 C 16 O 2 , 16 O 12 C 18 O, and 16 O 12 C 17 O lines at ϳ2311.8 cm −1 . High sensitivity was achieved by means of wavelength modulation spectroscopy with second-harmonic detection. The experimental reproducibility in the short and long terms was deeply investigated through the accurate analysis of a large number of spectra. In particular, we found a short term precision of 0.5‰ and 0.6‰, respectively, for 18 O/ 16 O and 17 O/ 16 O isotope ratios. The occurrence of systematic deviations is also discussed.