Spreading Transition of a Liquid Film

and lone-pair electrons of its oxygen atom attached to the various sites in the latter case. The absorbance of the a band increased until the BET monolayer capacity of 1.1 mmol g-' was reached but stayed constant above this water content. The reason for this result could be that these free OH groups exist only on the surface of adsorbed layers or may remain inside the layer without hydrogen bonding. A band at 3691 cm-l in spectrum 4 of Figure 6 appeared simultaneously with band a. Therefore, this 3691-cm-' band may be the fundamental stretching vibration band of adsorbed water, since the wavenumber of this band is close to those of the fundamental stretching vibration of water vapor a t 3756 and 3652 cm-1.22 A model of the configuration of the surface P-OH groups and adsorbed water is postulated in Figure 8, as a summary of the discussion described above.