PICOSECOND TIME-RESOLVED IR-UV PUMP-PROBE SPECTROSCOPIC STUDY ON VIBRATIONAL ENERGY RELAXATION OF BENZENE DIMER AND TRIMER IN THE CH STRETCHING REGION
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Ohio State UniversityAbstract:
Vibrational energy relaxation (VER) in the CH stretching region of benzene dimer (Bz$_2$) and trimer (Bz$_3$) has been studied by IR-UV pump-probe spectroscopy in supersonic beams. Firstly, we investigated isotope-substituted {\em hd} heterodimer, where {\em h}=C$_6$H$_6$ and {\em d}=C $_6$D$_6$, because the Stem and Top sites in the {\em hd} dimer can be site-selectively excited, different from {\em hh} homodimer. The two {\em h}(stem){\em d}(top) and {\em h}(top){\em d}(stem) isomers show remarkable difference in the lifetimes of intracluster vibrational energy redistribution (IVR). In the transient UV spectra, we observed a broad electronic transition due to the bath modes. The time evolutions of the bath modes can be described by a three step VER model involving IVR and vibrational predissociation (VP). This model was also confirmed by the observed rise profile of the Bz fragment. Secondly, we investigated {\em hh} homodimer. The {\em hh} homodimer shows the stepwise VER process with time constants similar to those of the {\em hd} dimer, suggesting a very weak excitation-exchange coupling of the vibrations between the two sites of the {\em hh} dimer. Finally, we found that Bz$_3$ also exhibits the stepwise VER process, though each step is faster than Bz$_2$.
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Author Institution: Department of Chemistry, Graduate School of Science, Hiroshima University, Higashi-Hiroshima, 739-8526, Japan
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ArticleOther Identifiers:
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