Vibrational dephasing and the Raman non-coincidence effect of CHBr3 in isotopic dilution

The yl (C-H) stretching mode of CHBr3 was investigated in the solvent CDBr3 at room temperature using three-colour femtosecond CARS and scanning multi -channel Raman difference spectroscopy (SMT-RDS), Small but measurable blue shifts (less than or equal to 1 cm(-1)) of the isotropic part of the Raman scattering relative to the anisotropic component and upon isotopic dilutio n are the clear signatures of the Raman non-coincidence effect and isotopic lineshift, respectively. The experimental results are discussed in terms o f theoretical models providing insight in the intermolecular coupling mecha nisms. The measured shift Delta nu(ID) = 0.73 +/- 0.02 cm(-1) upon isotopic dilution is found to be dominated by the attractive interaction and is to be compared with the non-coincidence effect of Delta nu(NCE) = 1.02 +/- 0.0 5 cm(-1) for the neat liquid. A 5% decrease in the dephasing rate 1/T-2 and a similar change in the linewidth upon infinite dilution are observed and semi-quantitatively explained via repulsive intermolecular interaction in a ccordance with an estimate of the corresponding (small) wavenumber shift. C opyright (C) 2000 John Wiley & Sons, Ltd.