Mode dependent intracluster vibrational energy redistribution rate in size-selected benzonitrile-(CHCl3)(n=1-3) clusters

The rate constants of intracluster vibrational energy redistribution (IVR) of benzonitrile-(CHCl3)(1) for the 12(1) (1000 cm(-1)), 1(1) (760 cm(-1)), and 6a(1) (460 cm(-1)) levels have been measured by time-resolved stimulate d Raman-UV double resonance spectroscopy. It was found that the observed ra te constants are independent of the energies but strongly dependent on the vibrational modes. In order to find a relationship between the structure an d the IVR rate, structures of benzonitrile-(CHCl3)(n=1-3) have been determi ned based on the results of the Raman spectra and the high resolution S-1-S -0 electronic spectra for the size-selected clusters, and ab initio MO calc ulations. The Raman spectra were observed for both CHCl3 and benzonitrile s ites. It was found that the CH stretching vibration of the CHCl3 moiety sho wed a higher frequency shift in the clusters, whose magnitude depends on th e binding site to benzonitrile. For the benzonitrile moiety, the Raman spec tra of CH stretch (nu (2)), CN stretch (nu (CN)), ring breathing (nu (12) a nd nu (1)), and CCC in-plane bending (nu (6a)) vibrations were investigated . From those results, it was concluded that the clusters have the form such that the CH hydrogen of the first CHCl3 is hydrogen-bonded to the N end of the CN group, while second and third CHCl3 are hydrogen-bonded to the phen yl ring. The observed mode dependence of the IVR rate constants will be dis cussed based on the cluster structure and the vibrational motion. (C) 2001 American Institute of Physics.