Temperature Effects on the Structure and Dynamics of Isomeric Pentanols by IR and Raman Spectroscopy

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Abstract
We present IR absorption, polarized and depolarized Raman scattering data in n-pentanol and in 2methyl-2butanol. The measurements, performed over a wide temperature range, concern the fundamental O—H stretching vibrations. The experimental results confirm that intermolecular H-bonding effects play the main role in determining the shape and the evolution with T of the spectra. The deconvolution of the polarized Raman spectra in symmetric bands gives useful information concerning the dynamical properties of these systems. The analysis of the frequency shifts, the broadenings and the relative intensity variations with respect to the isolated O—H stretching bands confirm the existence of molecular aggregates with different spatial and/or topological conformations. The close analogy found for appropriately reduced IR absorption and depolarized Raman spectra proves that a vibrational density of states (VDOS) for both alcohols exists. These spectral features can be rationalized in terms of cooperative models recently used to interpret the vibrational dynamics of structured systems.