Vibrational coherence of S1 trans-stilbene in solution observed by 40-fs-resolved absorption spectroscopy:: comparison of the low-frequency vibration appearing in the frequency-domain and time-domain spectroscopies

Temporal behavior of the S-n <-- S-1 absorption of trans-stilbene was measured in solution with a = 40-fs time resolution. An underdumped oscillation due to the S-1 vibrational coherence was observed in the early times. The Fourier-transform analysis showed that the S-1 in-plane deformation mode (v(25), 200 cm(-1)) gives rise to the oscillatory signal. This mode-specificity results from significant displacements among the S-0, S-1, and S-n potentials along the corresponding vibrational coordinate. It is shown that the amplitude of the vibrational coherence signal is semi-quantitatively related to the intensities in the two frequency-domain spectroscopies, the S-1 <-- S-0 absorption and the S-1 resonance Raman. (C) 2000 Published by Elsevier Science B.V.