We applied a photoacoustic spectroscopy technique to isotope ratio measurements of <sup>16</sup>O and <sup>18</sup>O in water-vapor samples, using a pulsed tunable dye laser pumped by a Nd:YAG laser. The fourth overtone bands (4ν<sub>OH</sub>) of water molecules near 720 nm were investigated. We identified the absorption lines of H<sub>2</sub><sup>16</sup>O and H<sub>2</sub><sup>18</sup>O in the photoacoustic spectra that we measured by using an <sup>18</sup>O-enriched water sample and the HITRAN database. We measured the difference in the <sup>18</sup>O/<sup>16</sup>O isotope ratios for normal distilled water and Antarctic ice, using the photoacoustic method. The value obtained for the difference between the two samples is δ<sup>18</sup>O = −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 δ<sup>18</sup>O = −28 ∓ 2‰. This method is demonstrated to have the potential of a transportable system for <i>in situ</i> and quick measurements of the H<sub>2</sub><sup>18</sup>O/H<sub>2</sub><sup>16</sup>O 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)