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 Sn←S1 absorption of trans-stilbene was measured in solution with a ≈40-fs time resolution. An underdumped oscillation due to the S1 vibrational coherence was observed in the early times. The Fourier-transform analysis showed that the S1 in-plane deformation mode (ν25, 200 cm−1) gives rise to the oscillatory signal. This mode-specificity results from significant displacements among the S0, S1, and Sn 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 S1←S0 absorption and the S1 resonance Raman.