Vibrational spectra of matrix isolated alkali metal chlorate ion pairs

The alkali metal chlorates have been found to volatilize without dissociation so that matrix isolation of the molten salt vapors permits spectroscopic study of the vibrational modes of the chlorate anion in the monomeric M+ClO3− ion pairs. The spectra clearly show evidence of the cation polarization of the anion since well-separated doublets have been observed for ν3 and ν4, both of which are doubly degenerate for the undistorted anion. However, the ν3 splitting is small compared to the splitting of the analogous mode for the nitrate monomers, M+NO3−, and also by contrast, the chlorate splitting is insensitive to a change in metal cation. The vibrational data have been used to deduce a modified valence force field for the ion pairs which shows a strong anion polarization, increasing through the series from potassium to lithium. Nevertheless, the force fields confirm that the anion distortion is relatively small compared to that reported for the nitrate anion in the M+NO3− monomers. Some infrared and Raman bands have also been detected for the dimeric (MClO3)2 species, but with the possible exception of KClO3, the dimer concentration in the matrices was quite low suggesting that the dimer is only a minor component of the molten chlorate vapors.