Concentration-dependent Raman study of noncoincidence effect in the NH2 bending and C = O stretching modes of HCONH2 in the binary mixture (HCONH2+CH3OH)

The isotropic and anisotropic parts of the Raman spectra of NH(2) bending and nu(C=O) stretching modes of HCONH(2) in a hydrogen-bonding solvent, methanol, at different concentrations have been analyzed carefully in order to study the noncoincidence effect (NCE). In neat HCONH2. the experimentally measured values of noncoincidence Delta nu(nc) are similar to 11 and similar to 18 cm(-1) for the NH(2) bending and v(C=O) stretching modes, which reduce to 0.45 and 1.14 cm(-1), respectively at the concentration of HCONH2 in mole fraction, chi(m) = 0.1. The experimental results have been explained on the basis of two models, namely, the microscopic prediction of Logan and the macroscopic model of Mirone and Fini. The relative success of the two models in explaining the experimental data for both the modes have been discussed. It has been observed that in case of the nu(C=O) stretching vibrational mode the Logan model can reproduce the experimental data rather precisely, whereas in the case of the NH(2) bending mode, Mirone and Fini model yields more accurate results. Copyright (C) 2006 John Wiley & Sons, Ltd.