EXCITON INTERPRETATION OF VACUUM-ULTRAVIOLET ABSORPTION SPECTRA OF SATURATED ORGANIC POLYMERS

A recent application of the molecular exciton theory to the a bond absorptions of simple gaseous alkanes has prompted the extension of the theory here to saturated organic polymers in the solid phase. The theory explains the experimentally observed insensitivity of the absorption spectra to changes in polymer chain conformation and, in the case of simple alkanes, to changes from gas to solid phase. It also explains the observed similarity between the low-energy portions of the absorption spectra of such diverse materials as diamond and gaseous alkanes. The exciton energy levels of polyethylene, polypropylene, and diamond are calculated and are found to give very reasonable agreement with the previous experimental data on polyethylene and diamond, and with the absorption spectrum of polypropylene which is presented here between 2500 and 584 A. The polarizations of the optically allowed transitions are also obtained but no experimental data is yet available on these. The possible implications of this exciton interpretation to the radiation chemistry of saturated hydrocarbon polymers are briefly discussed.