RAMAN-SPECTROSCOPIC STUDIES ON THE INTERACTION BETWEEN COUNTERIONS AND POLYPHOSPHATE ION

Interactions between polyphosphate ions and several cations, such as Na+, Cs+, Ca2+, and Ba2+ were investigated by means of Raman spectroscopy. A Raman band assigned to the PO vibrational stretching mode of polyphosphate neutralized by (CH3)4NOH in solution shifted to the higher frequency side with increasing concentration of added cations, but no frequency shift was observed in NaH2PO4 solution. The magnitude of the frequency shift is in the order of Ca2+, Ba2+, Na+, and Cs+. The Raman intensity varied with the addition of the cations. However, the addition of tetramethylammonium salt did not affect the PO stretching mode of polyphosphate. It is concluded from these results that the counterions closely approach polyions so as to perturb the force constant and the polarizability derivative of the PO bonds and interaction between polyphosphate ion and cations is not purely covalent.