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MO: Fachverband Molekülphysik

MO 22: Femtosecond Spectroscopy 3

MO 22.4: Vortrag

Freitag, 27. März 2015, 11:45–12:00, PH/HS1

Towards multi-dimensional Raman spectroscopy of excited electronic states in the time domain — •Torsten Wende, Christoph Schnedermann, Matz Liebel, and Philipp Kukura — Physical & Theoretical Chemistry Laboratory, South Parks Road, Oxford OX1 3QZ

Many biological and chemical processes rely on an efficient transfer of photon energy into specific atomic motion. Following the nuclear motion directly after photoexcitation provides valuable structural information to elucidate the mechanism that governs the energy flow throughout a molecule. We have developed a time-domain approach for measuring time-resolved excited-state Raman spectra by means of population-controlled impulsive vibrational spectroscopy. Using an ultrashort actinic (<15 fs) and impulsive (<10 fs) pump pulse in combination with a narrowband dump control pulse allows us to experimentally isolate excited-state vibrational coherence and follow its temporal evolution. Here, we study the fast internal conversion (<100 fs) from the S2 into the S1 electronic state in diphenyl-octatetraene. The time-resolved Raman spectra reveal that vibrational coherence is efficiently transferred from S2 into S1. We observe large amplitudes in the 850, 1300 and 1550 cm-1 modes which decay according to the S2 lifetime, while the remaining modes decay primarily with the lifetime of S1. Extraction of a 2D correlation map exhibits signatures of vibrational coupling indicated by multiple cross-peaks between low-frequency modes and selected high-frequency modes.