We present the first direct measurement of dynamic behavior of ions in an aqueous solution at high temperatures and pressure using Raman spectroscopy. We have studied the N-O symmetric stretching mode at high temperatures up to 340 degrees C and at a high pressure of 30 MPa. The Raman spectra of 1.3 M aqueous zinc nitrate solution have been analyzed by curve fitting. The zinc ion forms two species. In one species Zn2+ is bound more strongly to the NO3-, and in the other Zn2+ is bound more strongly to H2O. The ratio of the former to the latter remains unaltered with temperatures below 300 degrees C, but above 300 degrees C the ratio increases significantly. The average number of water molecules bound to Zn2+ (n(H2O)) is estimated using the intensity of peak frequency of the symmetric stretching mode of the haxaaquazinc(II) cation. As the temperature increases, the n(H2O) gradually decreases, but above 300 degrees C it shows a large decrease, suggesting the displacement of water molecules from the first solvation shell around Zn2+ and the concomitant entry of NO3- into the shell. The perpendicular orientational relaxation time (tau(perpendicular to)) decreases significantly with temperature; the values of tau(perpendicular to) were 1.86 and 0.25 ps, respectively, at 20 and 340 degrees C. The Arrhenius plot gives two activation energies, 2.1 kcal mol(-1) below 300 degrees C and 6.4 kcal mol(-1) above 300 degrees C. The activation energy for the orientational motion, 6.4 kcal mol(-1), is larger than that for orientational motion of water, 4-5 kcal mol(-1), and we assume that orientational motion of the anion above 300 degrees C requires the breaking of water-water hydrogen bonds. Furthermore, the experimental values of the perpendicular diffusion constant (D-perpendicular to) at higher temperatures than 300 degrees C are in agreement with those of D-i calculated from the slightly damped free-rotor (SDFR) model, and the rotation around the C-3 axis of the anion is confirmed to proceed rapidly and approach that in the free dilute gas phase.