Determination of the deuterium abundance in water using a cw chemical DF laser

This paper describes a new method for the determination of the deuterium content in water samples. The absorption of the radiation of a cw deuterium fluoride laser by HDO in water vapor is measured by means of a nonresonant spectrophone (optoacoustic detector). This method enables one to evaluate the isotope ratio of hydrogen in a rather simple and straightforward way. Advantage is taken of the fact that HDO absorbs some of the DF laser lines whereas H₂O shows no absorption. Due to the small concentration in natural water deuterium is practically entirely present as HDO. Therefore a selective determination of the deuterium content is possible. In the course of the investigation the absorption coefficients of HDO for the different laser lines were determined. It was thereby established that there exists a strong coincidence of an HDO absorption line with the 2P2 DF laser line. The detection sensitivity of the method was then examined for some selected laser lines. The concentration of HDO in natural water samples could be determined with an accuracy of better than 10%. The experiments, however, show that with appropriate improvements it should be possible to achieve an accuracy of better than 1%. This makes the method very interesting as an analytical tool in hydrology.