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

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 similar 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 MP2/cc-pVTZ (for S-0) and XMCQDPT2/cc-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. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4769971]