Abstract

We applied a photoacoustic spectroscopy technique to isotope ratio measurements of ¹⁶O and ¹⁸O in water-vapor samples, using a pulsed tunable dye laser pumped by a Nd:YAG laser. The fourth overtone bands (4ν _OH) of water molecules near 720 nm were investigated. We identified the absorption lines of H₂ ¹⁶O and H₂ ¹⁸O in the photoacoustic spectra that we measured by using an ¹⁸O-enriched water sample and the HITRAN database. We measured the difference in the ¹⁸O/¹⁶O isotope ratios for normal distilled water and Antarctic ice, using the photoacoustic method. The value obtained for the difference between the two samples is δ¹⁸O = -32 ± 16‰, where the indicated deviation was a 1σ value among 240-s measurements, whereas the value measured with a conventional isotope mass spectrometer was δ¹⁸O = -28 ± 2‰. This method is demonstrated to have the potential of a transportable system for in situ and quick measurements of the H₂ ¹⁸O/H₂ ¹⁶O ratio in the environment.

© 1998 Optical Society of America

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