“…Overall spectral pattern of the FSRS spectrum taken in this work (Fig. 5b) is quite consistent with the previously reported S 1 resonance Raman spectra of the same molecules 28,29 . As expected, the spectral resolution of the FSRS spectrum obtained in the 2nd-order DPGF setup is certainly better than that obtained in the 1st-oder DPGF (Fig.…”
Prolongation of the picosecond Raman pump laser pulse in the femtosecond stimulated Raman spectroscopy (FSRS) setup is essential for achieving the high spectral resolution of the time-resolved vibrational Raman spectra. In this work, the 2nd-order diffraction has been firstly employed in the double-pass grating filter technique for realizing the FSRS setup with the sub-5 cm−1 spectral resolution. It has been experimentally demonstrated that our new FSRS setup gives rise to a highly-resolved Raman spectrum of the excited trans-stilbene, which is much improved from those reported in the literatures. The spectral resolution of the present FSRS system has been estimated to be the lowest value ever reported to date, giving Δν = 2.5 cm−1.
“…Overall spectral pattern of the FSRS spectrum taken in this work (Fig. 5b) is quite consistent with the previously reported S 1 resonance Raman spectra of the same molecules 28,29 . As expected, the spectral resolution of the FSRS spectrum obtained in the 2nd-order DPGF setup is certainly better than that obtained in the 1st-oder DPGF (Fig.…”
Prolongation of the picosecond Raman pump laser pulse in the femtosecond stimulated Raman spectroscopy (FSRS) setup is essential for achieving the high spectral resolution of the time-resolved vibrational Raman spectra. In this work, the 2nd-order diffraction has been firstly employed in the double-pass grating filter technique for realizing the FSRS setup with the sub-5 cm−1 spectral resolution. It has been experimentally demonstrated that our new FSRS setup gives rise to a highly-resolved Raman spectrum of the excited trans-stilbene, which is much improved from those reported in the literatures. The spectral resolution of the present FSRS system has been estimated to be the lowest value ever reported to date, giving Δν = 2.5 cm−1.
“…This band has been assigned to the central CdC stretch vibration. 13 The time-resolved Raman spectra in the CdC stretch region are shown in Figure 1 for a chloroform solution. The intensity of each Raman band is normalized so that the time dependence of the peak position and the band shape can be better compared.…”
The excess energy dissipation process of photoexcited S 1 trans-stilbene in solution has been studied with picosecond time-resolved Raman spectroscopy. The peak position of the 1570-cm -1 band (CdC stretch) is shown to be useful as an indicator of picosecond temperature changes; a picosecond time-resolved Raman spectrometer can be regarded as a "picosecond Raman thermometer". The cooling rates of S 1 trans-stilbene thus observed in 10 different solvents show a strong correlation with the thermal diffusivities of the bulk solvents. Based on this observation, a simple numerical model is proposed for the solute-solvent energy dissipation process in solution. The observed cooling kinetics are analyzed with this macroscopic model. It is concluded that the excess energy is first shared among the solute and the nearest solvent molecules in a few picoseconds or faster. The further heat conduction to outer-sphere solvent molecules determines the whole dissipation rate, which explains the observed correlation between the vibrational cooling rate and the thermal diffusivity of the solvent.
“…Wavenumbers of bands attributed to the S 1 species are indicated in the upright letters. (C) Representative Raman spectral pattern of trans -stilbene in the S 1 state in n -hexane solution. , 2 (A) Infrared spectrum of trans -stilbene in the S 0 state in acetonitrile solution. The solvent bands are numerically removed.…”
Section: Resultsmentioning
confidence: 99%
“…It is of fundamental importance to reveal molecular structures of electronically excited states of this molecule, in order to discuss photoisomerization mechanisms. Various attempts have been made to obtain information on the structure of the lowest allowed electronically excited singlet (S 1 ) state, from vibrational analyses of electronic spectra in the gas phase − and from those of resonance Raman and transient Raman − spectra in solution. In the gas phase, the equilibrium structure of the S 1 state is considered to possess a center of inversion symmetry, which is also the case in the ground electronic (S 0 ) state. , Since the first two reports in 1983, , the transient Raman spectrum of tS in the S 1 state in solution is very well studied, − and the vibrational assignments of the totally symmetric Raman bands are quite well established. ,,,,,, However, information on the excited molecular structure in solution is still scant.…”
The picosecond transient infrared spectrum of the lowest excited singlet (S1) state of trans-stilbene in solution
has been recorded in the fingerprint region. Several absorption bands (molar absorption coefficients ε ≲ 100
mol-1 dm3 cm-1) attributable to in-plane vibrational modes of the S1 species have been observed. The tentative
assignments of the vibrational bands are described. Major spectral features are common between the infrared
spectrum taken in n-heptane solution and that in acetonitrile solution. The mutual exclusion rule between
infrared and Raman spectra of the S1 species seems to hold in n-heptane solution, which suggests a molecular
structure with a center of symmetry. On the other hand, additional weak infrared bands are found in acetonitrile,
whose positions coincide with those of the strong Raman bands of the S1 species. This result suggests that
the S1 species in acetonitrile is distorted slightly from the centrosymmetric structure. Polarized structures of
excited species stabilized in polar solvents are discussed in relation to the distorted S1
trans-stilbene in
acetonitrile.
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