B-band resonance Raman study of nitromethane in ethanol/water solvent

Abstract

We have obtained B-band resonance Raman spectra of nitromethane in an ethanol water mixed solvent. The spectra have been recorded at 298 K were the solvent is a liquid and at 77 K were the solvent forms a glass. The absorption spectra and resonance Raman intensities were simulated using wavepacket calculations and a simple model. The absorption and resonance Raman spectra as well as the simulation parameters were very similar for the liquid and glass spectra. This suggests that the ground and excited states in the first part of the Franck-Condon region are very similar for the liquid and glass solvent environments. However, there were some noticeable differences in the liquid and glass resonance Raman spectra. The glass Raman bands shift toward lower vibrational frequencies at higher vibrational quanta compared to the liquid Raman bands which indicates that attractive forces are larger for the glass compared to the liquid for the ground electronic state. The Raman bandwidths are smaller in the glass than the liquid which implies that ground state vibrational dephasing is smaller for the glass than the liquid.