The nature of the ‘free’ OH groups in water

The shoulder at the high‐frequency edge of the O‐H stretching bands in the Raman spectra of liquid water is suppressed by addition of about 12 mol% of hydrogen peroxide. This is further evidence for ‘free’ OH groups, i.e. non‐hydrogen‐bonded (NHB), in water, in contrast with liquid hydrogen peroxide. According to a new model, water contains two kinds of hydrogen bonds: the linear bonds (LHB), as in ice, and the bifurcated bonds (BHB) between three molecules. This upsets the ideal 1:1 ratio of proton donor to proton acceptor sites, creating a slight excess of the former, hence the ‘free’ OH groups. Their concentration at room temperature is only of the order of 1–2% from comparison with the spectra of the OH − ion in aqueous solutions. There are no ‘free’ H 2 O molecules in liquid water.