High pressure isotropic bandwidths and frequency shifts of the C–H and C–O modes of liquid methanol

The Raman bands of the C–H ν3 and C–O ν8 stretching modes of liquid methanol have been measured at temperatures ranging from 273 to 363 K and pressures from 10 bar to 4 kbar. The effects of density and temperature on the isotropic linewidth, peak frequency of the isotropic band, ν0 (ISO), and the difference δν between anisotropic ν0(VH) and ν0(ISO) band frequencies are reported and discussed qualitatively in terms of available theoretical models. It appears that repulsive interactions are responsible for the observed C–H line changes, and the Schweizer–Chandler (SC) model is used to evaluate frequency shift and bandwidth of the ν3 C–H mode after the effect of Fermi resonance coupling to the 2ν4 overtone was removed. In particular, the anomalous temperature and density dependence of the Raman band of the C–O stretching mode is noted and compared to the relatively typical behavior observed for the Raman line shape of the C–H mode.

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