UV-VISIBLE ABSORBENCY SPECTROSCOPY OF ORGANIC PROBES IN SUPERCRITICALWATER

UV-visible spectra of organic probes are reported in supercritical wat er (SCW) for the first time up to 440 degrees C and 5000 psia. Solvato chromic shifts in the pi-pi absorbance band of benzophenone are compa red with those of the n-pi band of acetone to characterize the dipola rity, polarizability, and hydrogen bond donor strength of water. In th e near-critical region (0.5 < rho(r) < 1.5), physical and hydrogen-bon ding interactions augment the density of water about each probe, relat ive to the bulk density. At 380 OC, hydrogen bonding persists at a den sity of only 0.1 g/mL but rapidly disappears at lower densities. Spect roscopic measurements of interactions between SCW and organic solutes at the molecular level provide new insights into solvent effects on ch emical reactions in SCW.