Near infrared spectra of water and aqueous solutions

Spectra ranging from 4000 to 12,500 cm−1 were obtained with H2O, D2O, D2OH2O mixtures, and solutions of these solvents containing various ionic species. The shapes and/or positions of these bands were influenced by both temperature and dissolved salts. In the 8300-cm−1 region, a pronounced band was observed at 8640 cm−1 with H2O near the boiling point, whereas with ice a broad but rather well-formed band was observed at 7990 cm−1. In H2O at room temperature or below a very broad and deformed band appeared at 8310 cm−1 with a distinct shoulder around 8600 cm−1, which became more apparent with an increase in temperature. The effect of dissolved species on the spectrum of H2O was very similar to the observed temperature effect, and the relative intensity of the absorption at 8640 cm−1 and at 8310 cm−1 seems to be indicative of the degree of “structure-breaking” or “structure-making” power of the dissolved species. The order of increasing structure-breaking (or decreasing structuremaking) power deduced from the spectra was C Cl− < Br− < I− < ClO4− and Li+ < Na+ < K+ < Cs+ < N(CH3)4+. This is in good agreement with the published results from measurement of other properties of solutions. Similar temperature and salt effects were also observed with other bands of H2O and D2O.