Vibrational dynamics of 1,3-propanediol in liquid, polycrystalline and glassy states: A Raman spectroscopic study

Vibrational transitions of 1,3-propanediol in liquid and crystal phases are assigned on the basis of Raman and infrared spectra of liquid and low temperature (295K-10K) Raman spectra which are presented here for the first time. In the crystal, there are four molecules per unit cell, each having a gGGg' conformation. The vibrations for the P2₁/n crystal phase having four molecules in the unit cell are obtained by an ab initio calculation using CRYSTAL09 program, and are in good agreement with the observed Raman bands. Observed bands in Raman spectrum of liquid are in proximity of those observed for crystal phase, and it is tempting to assign them as belonging mainly to gGGg' conformer. However, quantum chemical ab initio calculations provide basis to ascertain that tGG'g and tGGt are two conformers having lowest energy at the B3LYP/6-31++G(d,p) level of theory. Several bands that disappear from Raman spectrum of liquid on solidification (384, 872 and 1040 cm^-1) could give an insight into the nature of conformers present in liquid. Since the closest calculated vibrations are 386cm^-1 for tGG'g and 1043cm^-1 for tGG't conformer, we conclude that all three conformers: tGG'g, tGGt and gGGg', are present in the liquid.