The earlier work on the vibrational dynamics of trans-1,4-polyisoprene (beta-TPI) suffered from several infirmities. This work has been redone with all infirmities removed. It not only leads to a few different assignments but also better values of interactive constants. Two significant outcomes of the present work are; one change in the profile of the dispersion curves and repulsion between the two acoustic modes at the phase values away from the zone center. The present work leads to a fuller interpretation of observed spectra. Several observed unassigned modes have been accounted for due to the presence of regions of high density-of-states such as von Hove type singularities. Predictive values of heat capacity as a function of temperature are reported. (c) 2006 Elsevier Ltd. All rights reserved.