Excitation-energy dependence of transient grating spectroscopy in beta-carotene

Sugisaki, M., Fujiwara, M., Nair, S.V., Ruda, H.E., Cogdell, R.J. and Hashimoto, H. (2009) Excitation-energy dependence of transient grating spectroscopy in beta-carotene. Physical Review B, 80(3), 035118-035128. (doi: 10.1103/PhysRevB.80.035118)

Abstract

Transient grating (TG) signals from beta-carotene were measured at various excitation energies (wavelengths). Clear coherent oscillations with a period of a few tens of femtoseconds were observed when the excitation energy was tuned in the vicinity of the absorption edge. It was found that the TG signal is very sensitive to the excitation energy. When the TG signal is measured near the absorption maximum, following the coherent spike at the origin of the time axis, weak coherent oscillations are observed superimposed on a slowly varying background. The rise time of this slowly varying background is 0.4 ps and is followed by the slow decay with a 5 ps time constant. As the excitation energy is decreased the coherent oscillations become more prominent. The coherent oscillations and the slowly varying background become very weak again when the excitation energy is lower than the absorption edge. The TG signals were calculated using two sets of energy and Feynman diagrams to investigate possible pathways of the electronic internal conversion and vibronic decoherence processes. The modeling indicates that the vibronic coherence, initially established by pumping into the excited state S₂, instantaneously decays due to relaxation into an intermediate state S_x, which is located between S₂ and S₁. Possible interpretation of the nature of the S_x state is discussed

• Item Type: Articles
• Keywords: excited states, Feynman diagrams, nonradiative transitions, organic compounds, vibronic states
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Cogdell, Professor Richard
• Authors: Sugisaki, M., Fujiwara, M., Nair, S.V., Ruda, H.E., Cogdell, R.J., and Hashimoto, H.
• Subjects: Q Science > QH Natural history > QH345 Biochemistry; Q Science > QH Natural history > QH301 Biology
• College/School: College of Medical Veterinary and Life Sciences > School of Molecular Biosciences
• Journal Name: Physical Review B
• Journal Abbr.: Phys. Rev. B
• Publisher: American Physical Society
• ISSN: 1098-0121
• ISSN (Online): 1550-235X