Ultrafast dynamics of excited electronic states in nitrobenzene measured by ultrafast transient polarization spectroscopy

TL;DR

This study uses ultrafast transient polarization spectroscopy to explore the ultrafast electronic and wave-packet dynamics in nitrobenzene's excited states, revealing oscillatory behavior and state transitions.

Contribution

It extends optical Kerr effect spectroscopy to excited states, providing new insights into wave-packet dynamics and state dephasing in nitrobenzene.

Findings

Measured dephasing times show oscillations indicating wave-packet dynamics.

Wave-packet leaves the S1 state after three crossings with T2.

Supports theoretical models of excited state dynamics in nitrobenzene.

Abstract

We investigate ultrafast dynamics of the lowest singlet excited electronic state in liquid nitrobenzene using Ultrafast Transient Polarization Spectroscopy (UTPS), extending the well-known technique of Optical-Kerr Effect (OKE) spectroscopy to excited electronic states. The third-order non-linear response of the excited molecular ensemble is highly sensitive to details of excited state character and geometries and is measured using two femtosecond pulses following a third femtosecond pulse that populates the S1 excited state. By measuring this response 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 surface after three traversals of the inter-system crossing between the singlet S1 and triplet T2 states.