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 (4νOH) of water molecules near 720 nm were investigated. We identified the absorption lines of H216O and H218O 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 H218O/H216O ratio in the environment.
© 1998 Optical Society of America
Yutaka Matsumi, Masahiro Kishigami, Noriyuki Tanaka, Masahiro Kawasaki, and Gen Inoue, "Isotope 18O/16O Ratio Measurements of Water Vapor by use of Photoacoustic Spectroscopy," Appl. Opt. 37, 6558-6562 (1998)