Short-time photodissociation dynamics of nitrocyclopentane and nitrocyclohexane in the gas and solution phases from resonance Raman intensity analysis

Abstract

We have obtained B-band resonance Raman spectra of nitrocyclopentane and nitrocyclohexane in the vapour and in cyclohexane solution. The B-band resonance Raman spectra have most of their intensity in the nominal NO₂ symmetry stretch progression (nυ_NO2 ) and the initial Franck-Condon region dynamics changes occur mostly in the two N—O bonds. The absorption spectra and absolute Raman intensities were simulated using time-dependent wavepacket calculations and a simple model. These simulations suggest that very fast electronic dephasing (most probably due to predissociation and/or solvent collisions) competes with wavepacket motion out of the Franck-Condon region and vibrational motion of the rest of the molecule. This probably accounts for the observation that the B-band resonance Raman spectra of all the nitroalkanes studied so far appear very similar to one another.