Infra-red studies of water adsorbed on alkali halides

Source abstract

Abstract sed disks formed from finely powdered alkali halides act as matrices of large ce area on which the infra-red spectra of thin films of adsorbed water can be eniently studied. While completely transparent to visible and infra-red radia- electron micrographs show that the disks are mosaics of tiny crystals about n diameter packed very closely together. Satisfactory disks can be made from halide formed from Na, K, Rb and Cs with Cl, Br and I and spectroscopic ies have been made on water adsorbed on all twelve of these matrices. In this it is possible to follow the effect of the variation of size and electronegativity Le crystal ions on the water bands. The spectra have been examined under high lution both at room and liquid-air temperatures. Figure 40 shows the frequency of the strongest band in the 3000 to 3500 cm -1 ion plotted as ordinate against a unitary displacement of the negative halogen as abscissa. Straight lines join the bands with a common metal ion. The band responds to a modified asymmetrical stretching vibration of the water molecule. graphs indicate that the greatest shift in frequency relative to the free lecule is produced by the lattice with the halogen of greatest electronegativity the metal ion of lowest electropositive character. This indicates that the water attached by hydrogen bonding to the negative ions. This is supported by considerations of the relative size of the ions. The positive ions, particularly tho of sodium and potassium, being smaller, tend to be buried in the structure by t negative ions and are relatively inaccessible from the outside.