High overtone resonance Raman spectra of photodissociating nitromethane in solution

Abstract

Resonance Raman spectra of nitromethane have been obtained in cyclohexane, acetonitrile, and water solvents with excitation at 218 and 200 nm and in the vapor at 218 nm. Fully deuterated nitromethane has also been examined in both vapor and solution phases. Resolvable Raman lines are observed at energies up to 15 000 cm-1, which is approximately the lowest dissociation limit (to ground-state CH3O + NO). The spectra in solution and in the vapor are qualitatively similar in that overtone progressions in the NO2 symmetric stretch dominate, but the higher signal-to-noise ratio of the solution-phase data allows many weaker transitions to be observed as well. The vibrational frequencies and bandwidths are interpreted qualitatively to explore solvation effects on the ground-state potential surface. The resonance Raman intensities are modeled with a simple theoretical treatment employing wave packet propagation on a single electronic surface. This approach does a reasonable job of reproducing the relative and absolute solution-phase intensities, but some deviations between experimental and calculated combination band intensities are observed. © 1991 American Chemical Society.