Normal modes and their dispersion in poly(α-isobutyl-β-l-aspartate): I. 4/1 Helix

Poly(α-isobutyl-β-l-aspartate) is a stereoregular derivative of polyamides and exist in 4/1 and 13/4 helices. Normal mode analysis and their dispersion of the 4/1 form have been carried out using Urey–Bradley force constants. Apart from detailed assignment of modes, characteristic features of dispersion curves such as repulsion and cross-over have been explained as arising due to internal symmetry in the energy momentum space. Predictive values of heat capacity contribution from various types of modes are also reported.