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Profils de raies spectrales dans une spectroscopie électronique non linéaire

 

When studying ultrafast excited state dynamics by transient spectroscopy techniques one must consider dephasing processes which occur on a time scale comparable to the delay time between the pulses. The recorded spectra provide an averaged picture of the dynamics during the measurement (which can last several hundreds of femtoseconds). Nevertheless, a 5–10 femtoseconds resolution stems from the fact that different segments of the dynamics are averaged over depending on the delay times between the laser pulses which interact with the sample. To account for this time averaging in theoretical spectroscopy, it is crucial to model electronic fluctuations due to nuclear degrees of freedom, either intra- or intermolecular ( i.e. the spectral diffusion), and the fluctuations of the respective oscillator strengths during the underlying ultrafast dynamics. 

This article outline a computational approach for nonlinear electronic spectra, which accounts for the electronic energy fluctuations due to nuclear degrees of freedom and explicitly incorporates the fluctuations of higher excited states, induced by the dynamics in the photoactive state(s). The application is made to the two-dimensional electronic spectra of pyrene, a polycyclic aromatic hydrocarbon characterized by an ultrafast (few tens of femtoseconds) decay from the bright S-2 state to the dark S-1 state. The spectra for waiting times t(2) = 0 and t(2) = 1 ps demonstrate the ability of this approach to model electronic state fluctuations and realistic line shapes. Comparison with experimental spectra shows excellent agreement and allows us to unambiguously assign the excited state absorption features.
    

 Spectral lineshapes in nonlinear electronic spectroscopy

Nenov, A. ; Giussani, A. ; Fingerhut, B. P.. ; Rivalta, I.  ; Dumont, E. ; Mukamel, S. ; Garavelli, M.

 

PHYSICAL CHEMISTRY CHEMICAL PHYSICS

Volume: 17

Issue: 46

Pages: 30925-30936

DOI: 10.1039/c5cp01167a