Femtosecond Raman spectra of cis-stilbene and trans-stilbene with isotopomers in solution

摘要

Femtosecond stimulated Raman spectra of trans-stilbene (D0), its isotopomers D2, D10, D12, ~(13)C2 and of cis-stilbene in hexane are measured in the ground (S_0) and excited (S_1) electronic states. The ground ~(13)C2 and excited D12 spectra are presented for the first time; the excited cis-spectra differ substantially from previously published ones. S_1 Raman bands of trans-stilbene are 20 cm ~(-1) wide corresponding to ~1 ps vibrational dephasing. For cis-stilbene the bands are broadened to 40 cm~(-1) reflecting a short excited-state lifetime of 0.3 ps, in agreement with transient absorption data. From a dynamic shift of the 1569 cm~(-1) band, pump-induced intramolecular cooling is estimated to be less than 20 K. Many S_1 Raman lines are detected for the first time. Vibrational spectra are calculated at MP2cc-pVTZ (for S_0) and XMCQDPT2cc-pVTZ (for S_1) levels of theory. Experimental and computational results can be used for a re-evalution of Rice-Ramsberger-Kassel-Marcus (RRKM) predictions for this famous photoisomeration reaction.