Vibrational Spectra and Structure of Macromolecules

Regents Of The University Of Michigan - Ann Arbor, Ann Arbor MI

Investigators

Abstract

The goal of this research program is to develop and apply more physically accurate potential energy functions for polymeric macromolecules than are presently available, in particular functions that, in addition to the usual prediction of structures and energies, give spectroscopically accurate reproduction of vibrational frequencies (which is not achieved by current standard functions). This is accomplished by the spectroscopically determined force field (SDFF) methodology previously developed in this laboratory. Under this proposal, current SDFFs will be extended to include polarization, which is very important in describing properties of polar groups such as amides. A new protocol for determining parameters in the energy function assures the avoidance of correlations and indeterminacy in these quantities. The newly developed formalism for molecular dynamics in internal coordinates (ICMD) will be implemented on macromolecular systems. The hydrocarbon SDFF will be applied to the analysis and resolution of questions concerning structural transitions and the origin of spectral bands in trans-1,4-polybutadiene and band splittings in cis- 1,4-polybutadiene. The SDFF to be developed for the amide group will be used to calculate the normal modes of nylons 6 and 66 to provide deeper insights into the analysis of vibrational and inelastic neutron scattering spectra of these polymers. The new ICMD formalism will be applied to calculations on crystalline polyethylene, with the particular goals of correcting published spectral intensity inaccuracies and of comparing spectral predictions from normal mode analysis with those from the Fourier transformation of the time-autocorrelation function of the dipole moment. In addition to its intellectual contributions, this research program will have broader impacts. New research results will be incorporated into advanced courses, and graduate students and postdocs will develop and report a more sophisticated understanding of an important area of science. The previous emphasis on involvement of women in the research program will continue. Advanced computer programs for analysis of properties of polymers will be made available to the scientific community. The more acurate theoretical understanding of properties will lead to advances in commercial polymer technology and the amide group aspect of the work have will an important impact in the study of biological systems.