Dynamics of the time-resolved stimulated Raman scattering spectrum in presence of transient vibronic inversion of population on the example of optically excited trans-β-apo-8′-carotenal

We have studied the effect of transient vibrational inversion of population in trans-beta-apo-8'-carotenal on the time-resolved femtosecond stimulated Raman scattering (TR-FSRS) signal. The experimental data are interpreted by applying a quantum mechanical approach, using the formalism of projection operators for constructing the theoretical model of TR-FSRS. Within this theoretical frame we explain the presence of transient Raman losses on the Stokes side of the TR-FSRS spectrum as the effect of vibrational inversion of population. In view of the obtained experimental and theoretical results, we conclude that the excited S-2 electronic level of trans-beta-apo-8'-carotenal relaxes towards the S-0 ground state through a set of four vibrational sublevels of S-1 state. (C) 2014 AIP Publishing LLC.