Is there a correlation between phase transitions of phenylacetylene in liquids and frozen matrices and vibrational dynamics? Original Research Article

Raman spectra of the ν8(C–CN) bending mode of acetonitrile and the νs(CC) stretching mode of phenylacetylene (PA) in acetonitrile liquid solutions and frozen matrices as a function of temperature have been recorded. Mechanisms of vibrational relaxation and band broadening in liquid and solid phases have been discussed. One of the goals of the paper is to develop the correlation between the phase transitions and mechanisms of vibrational dynamics. The vibrational dephasing of the νs(CC) mode of PA and the bending mode ν8(C–CN) of acetonitrile in solution seems to be governed by the coupling of the vibrational modes to internal rotations of the methyl group CH3 of acetonitrile. The behaviour around the phase transitions between 183 and 218 K with the sudden increase in bandwidths was explained as the result of the changes in the mechanisms of the internal rotation from hindered rotation in periodic potential to almost free rotation for higher temperatures.