Absolute resonance Raman intensity analysis of isopropyl nitrate in the condensed phase

The first resonance Raman spectra of isopropyl nitrate (IPN) are reported. Absolute resonance Raman scattering cross-sections for IPN dissolved in cyclohexane and acetonitrile are measured at excitation wavelengths spanning the strong pi-pi* absorption located at similar to200 nm. Resonance enhancement is observed for seven vibrational coordinates, all involving the -ONO2 chromophore, demonstrating that the photoinduced excited-state structural evolution is dominated by structural changes localized to the -ONO2 group. The absorption and absolute resonance Raman cross-sections are modeled using the time-dependent formalism for absorption and Raman scattering. This analysis demonstrates that the photoinitiated excited-state structural-relaxation dynamics are multidimensional, and consistent with N-O bond cleavage. This observation is consistent with N-O bond dissociation being the dominant photodissociation pathway for larger (e.g., three or more carbon atoms) alkyl nitrates. Comparison of the results in cyclohexane and acetonitrile reveals that the excited-state structural evolution is solvent dependent. This observation suggests that the photoproduct formation dynamics of IPN are dependent on the environment in which the chemistry occurs.