APPLICATIONS OF LASER PHOTOACOUSTIC-SPECTROSCOPY USING AN OPTICAL PARAMETRIC OSCILLATOR TO THE STUDY OF COMPLEXATION EQUILIBRIA IN DILUTE AQUEOUS-SOLUTIONS

A 30 Hz YAG laser pumped, narrow-line, optical parametric oscillator ( OPO) has been used to investigate the chemical states of selected comp ounds in aqueous solution. The OPO system has the advantage that it ca n scan wavelengths over large ranges without significant loss of outpu t power. The visible spectra of rare earth complexes in dilute aqueous solutions (as chemical analogs for the actinides) have been studied a nd preliminary qualitative results for erbium acetate complexes at the 100 micromolar level are in good agreement with literature data. Quan titative measurements of the protonation constant for phenol red at th e 100 nanomolar level were measured. The particular implementation of the OPO system used in this work introduced a number of spectral artif acts due to optical signal overlap with near-infrared water absorption bands. In addition, it was demonstrated that the concentration limiti ng factor for photoacoustic spectroscopy is the intrinsic absorption o f water in the visible region of the spectrum.