Unpolarized and polarized Raman spectroscopy of nylon-6 polymorphs: a quantum chemical approach.

Exploiting the very recent potentialities of state-of-the-art quantum chemical simulations of crystalline solids, unpolarized Raman spectra of α and γ polymorphs of Nylon-6 obtained through periodic density functional theory calculations are presented for the first time. The computed spectra are compared with the experimental spectra reported in the literature and allow a detailed interpretation to be proposed of the patterns observed, identifying unambiguous Raman marker bands of the different phases. The calculations of single crystal directional intensities gave the further possibility to predict the polarization properties of the Raman spectra of these polymorphs: considering in particular the α phase, polarized Raman spectra have been computed and showed a very good agreement with measurements previously reported for uniaxially oriented samples.