Ultra-Violet Absorption Spectra of the Molecules H2O HDO and D2O

Journal/Book: Reprinted from Nature Vol. 187 No. 4732 pp. 138-139 July 9 1960. 1960;

Abstract: Department of Science Hatfield Technical College Herts. THE ultra-violet absorption spectrum of liquid water has been reported by various workers1-4. They found that absorption begins in the region of 200 mµ and increases with decreasing wave-length as far as the limit of measurement at 180 mµ. In view of the renewed interest in the photochemistry of aqueous systems at wave-lengths leas than 200 mµ this spectrum has been re-investigated together with that of the molecules HDO and D2O. The spectra of the purified materials were measured an a Hilger H700.308 ´Uvispek' equipped with a silica prism transmitting down to 185 mµ. At wave-lengths less than 195 mµ. it was found to be essential to render the entire optical path free from oxygen the gas having strong absorption in this region5. This was done by modifying the Instrument so that the optical system could be continuously flushed with oxygen-free nitrogen during measurements. Failure to observe this precaution led to spectra similar to those reported by Golding6 being observed. In order that spectra could be observed at various temperatures we have used a thermostatted cell-carriage in conjunction with Hilger high-transmittance 5-mm. and 1-cm. silica cells. Corrections for scattered light have been applied to all optical densities measured. The spectra of H2O HDO and D2O at 25°C. are shown in Fig. 1 and the corresponding spectra at 50° C. are shown in Fig. 2. The spectra of HDO were derived from the spectra of a 1 : 1 mixture of H2O and D2O the fractions of HDO present being calculated an the basis of the equilibrium constants for the exchange reaction: H2O + D2O ? 2HDO which have been reported by Urey 7. As can be seen from the spectra there are significant differences in the absorption coefficients of H2O HDO and D2O at any given wave-length and also the spectra are markedly dependent an temperature. The shape of the spectrum of H2O is in agreement with the previously reported work but the value of 1 x 46 cm-1 for for water at 185 mµ at 25° C. is higher than the previously reported value of 1 2 cm-1 (ref. 8). This we consider to be due to the greater HDO and D2O will be of use in the Interpretation of results of photochemical investigations of systems containing these species. The observed dependence an temperature has been noted by Golding6. We have investigated this effect in several systems in which hydrogen-bonding is known to be present. ... ___MH

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