INFRARED INTENSITIES OF LIQUIDS .20. THE INTENSITY OF THE OH STRETCHING BAND OF LIQUID WATER REVISITED, AND THE BEST CURRENT VALUES OF THE OPTICAL-CONSTANTS OF H2O(1) AT 25-DEGREES-C BETWEEN 15,000 AND 1 CM(-1)

The previously reported nonreproducibility of the intensity of the OH stretching band of liquid water has been explored. It was found that i t can be eliminated in measurements with the Circle(R) multiple ATR ce ll by ensuring that the ATR rod is coaxial with the glass liquid holde r. It was also found that normal laboratory temperature variations of a few degrees change the intensity by less than or equal to similar to 1% of the peak height. A new imaginary refractive index spectrum of w ater has been determined between 4000 and 700 cm(-1) as the average of spectra calculated from ATR spectra recorded by four workers in our l aboratory over the past seven years. It was obtained under experimenta l and computational conditions superior to those used previously, but is only marginally different from the spectra reported in 1989. In par ticular, the integrated intensities of the fundamentals are not change d significantly from those reported in 1989. The available imaginary r efractive index, k, values between 15,000 and 1 cm(-1) have been compa red. The values that are judged to be the most reliable have been comb ined into a recommended k spectrum of H2O(l) at 25 degrees C between 1 5,000 and 1 cm(-1), from which the real refractive index spectrum has been calculated by Kramers-Kronig transformation. The recommended valu es of the real and imaginary refractive indices and molar absorption c oefficients of liquid water at 25 +/- 1 degrees C are presented in gra phs and tables. The real and imaginary dielectric constants and the re al and imaginary molar polarizabilities in this wavenumber range can b e calculated from the tables. Conservatively estimated probable errors of the recommended k values are given. The precision with which the v alues can be measured in one laboratory and the relative errors betwee n regions are, of course, far smaller than these probable errors. The recommended k values should be of considerable value as interim standa rd intensities of liquid water, which will facilitate the transfer of intensities between laboratories.