UV-VISIBLE ABSORBENCY SPECTROSCOPY OF ORGANIC PROBES IN SUPERCRITICAL WATER

UV-visible spectra of organic probes are reported in supercritical water (SCW) for the first time up to 440 degrees C and 5000 psia. Solvatochromic shifts in the pi-pi* absorbance band of benzophenone are compared with those of the n-pi* band of acetone to characterize the dipolarity, polarizability, and hydrogen bond donor strength of water. In the near-critical region (0.5 < rho(r) < 1.5), physical and hydrogen-bonding interactions augment the density of water about each probe, relative to the bulk density. At 380 OC, hydrogen bonding persists at a density of only 0.1 g/mL but rapidly disappears at lower densities. Spectroscopic measurements of interactions between SCW and organic solutes at the molecular level provide new insights into solvent effects on chemical reactions in SCW.