The aggregation of dihydrogen phosphate ion has been studied by Raman spectroscopy during serial dilution of highly concentrated (5 M) solutions. Factor analysis has been used to recover monomer and aggregate spectra from families of 600-2000 spectra obtained during dilution to about 0.1 M. Spectra of the free aquated dihydrogen phosphate ion and its dimer, trimer, and tetramer have been obtained. There is some evidence for the existence of longer chain aggregates. The serial dilution procedure has been verified by dilution of 2.3 M glycine solution. Only spectra of monomer and dimer ions are recovered. For the well-understood glycine system, the band positions and intensities and the dimerization concentration-dependence are in agreement with previously reported values.
Jeremy M. Shaver, Kenneth A. Christensen, Jerilyn A. Pezzuti, and Michael D. Morris, "Structure of Dihydrogen Phosphate Ion Aggregates by Raman-Monitored Serial Dilution," Appl. Spectrosc. 52, 259-264 (1998)