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

• Published in: arXiv.org 2019-12
• Main Authors: Thurston, Richard, Brister, Matthew M, Tan, Liang Z, Champenois, Elio G, Bakhti, Said, Muddukrishna, Pavan, Weber, Thorsten, Belkacem, Ali, Slaughter, Daniel S, Shivaram, Niranjan
• Format: Article
• Language: English
• Subjects: Electron states; Excitation; Excitation spectra; Femtosecond pulses; Nitrobenzene; Nonlinear response; Polarization; Spectrum analysis
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1912.12902

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.