SPECTRA OF WATER IN THE NEARINFRARED AND MIDINFRARED REGION

Spectra of water have been acquired in the mid-infrared (MIR) and the near-infrared (NIR) region in the temperature range 2-96 degrees C and 4-52 degrees C, respectively. Loading plots from partial-least-square s regression were used to locate isosbestic points in the spectral ban ds of water. By means of least-squares, the original spectral profiles have been resolved into two spectra, one increasing and the other dec reasing with temperature. Concentration profiles of the two structural ly different water associations, for the investigated temperature rang e, were obtained by use of evolutionary curve resolution and first-ord er differentiation of the MIR spectra. Utilising information from the concentration profiles obtained in the MIR, the NIR spectra were resol ved. Relative concentrations were obtained using spectral intensities from the isosbestic points. The complexity in both the fundamental and overtone region of the spectra shows that both structures of water ar e involved in H-bonding. This result indicates a pseudo-first-order re action in water, either between an open and a more dense state, or bet ween a rigid, strongly H-bonded state and a more loosely H-bonded stat e. The cross-correlation pattern between the two regions can be ascrib ed to the temperature-induced variation in the concentration of the tw o associations.