Measurement of the isotopic ratio distribution of HD¹⁶O and H₂¹⁶O in the 20–38 km altitude range from far‐infrared spectra

The altitude distribution of the isotopic ratio between HD 16 O and H 2 16 O in the stratosphere is derived by retrieving the mixing ratio profiles (from 20 km to 38 km of altitude) of the two isotopic species from far‐infrared emission spectra. The measurements were made with a balloon‐borne Fourier Transform Spectrometer capable of 0.0025 cm −1 spectral resolution during the IBEX 92 campaign. The retrievals were carried out using the global‐fit procedure on a statistically significant number of spectra for each isotope, in the 40–75 cm −1 spectral region. This measurement determines the D/H ratio in stratospheric water over an altitude range larger than that of previous measurements. The value of the HD 16 O/H 2 16 O ratio, normalized to the standard value, ranges from 0.4 to 0.5 (with a 10% random error) in the altitude range studied and is in good agreement with the values previously measured.