Resonance Raman study of the solvation of p-nitroaniline in supercritical water

Resonance Raman spectra of p-nitroaniline (pNA) have been measured in various states of water. The relative intensities of two bands assigned to the NO2 stretching mode show a large temperature dependence along the 30.4 MPa isobar between ambient temperature and 669 K. Along the supercritical isotherm at 668.5 K, the higher frequency band shifts by 8 cm(-1) over the accessible density range (0.3-1.7 rho(c)). We also performed density-functional calculations of the Raman spectra of water clusters of pNA. The calculated changes in electronic structure and Raman spectra with cluster size are used to rationalize these experimental observations. (c) 2006 Elsevier B.V. All rights reserved.