posted on 2020-03-19, 13:07authored byRichard Thurston, Matthew M. Brister, Liang Z. Tan, Elio G. Champenois, Said Bakhti, Pavan Muddukrishna, Thorsten Weber, Ali Belkacem, Daniel S. Slaughter, Niranjan Shivaram
We investigate ultrafast dynamics
of the lowest singlet excited
electronic state in liquid nitrobenzene using ultrafast transient
polarization spectroscopy, extending the well-known technique of optical
Kerr effect spectroscopy to excited electronic states. The third-order
nonlinear response of the excited molecular ensemble is measured using
a pair of femtosecond pulses following a third femtosecond pulse that
populates the S1 excited state. By measuring this response, which is highly sensitive to details
of the excited state character and structure, as a function of time
delays between the three pulses involved, we extract the dephasing
time of the wave packet on the excited state. The dephasing time,
measured as a function of time delay after pump excitation, shows
oscillations indicating oscillatory wave packet dynamics on the excited
state. From the experimental measurements and supporting theoretical
calculations, we deduce that the wave packet completely leaves the
S1 state potential energy surface after three traversals
of the intersystem crossing between the singlet S1 and
triplet T2 states.