The Vibrational analysis of polyethylene terephthalate, polyethylene‐d4 terephthalate, and polyethylene terephthalate‐d4 has been carried out using a valence force field calculated from the infrared and Raman spectra of a series of low molecular weight aromatic esters. The Raman spectra for polyethylene‐d4 terephthalate and polyethylene terephthalate‐d4 are presented and band assignments for these compounds and polyethylene terephthalate are discussed.
The Raman scattering in crystalline polyethylene, deuterated polyethylene, and n-paraffins has been investigated as a function of temperature. Crystal-field splitting of the A1G methylene bending mode observed at room temperature increases at − 160°C in both polyethylene and deuterated polyethylene. No splitting of the B2G skeletal stretching mode and the B3G methylene twisting modes in polyethylene is observed at room temperature, but the two components of the space group fundamental are resolved at − 160°C. Similarly, splitting of the B2G methylene wagging mode in deuterated polyethylene is observed at − 160°C but not at room temperature. The observed crystal-field splittings are discussed in terms of splittings calculated from repulsive forces between hydrogen atoms on neighboring chains in the polyethylene crystal.
With the aid of newly obtained Raman data, a normal coordinate analysis has been performed on the polytetrafluoroethylene (PTFE) molecule. Calculations were made for three different helix models including the 13/6, 15/7, and planar zigzag. The frequencies corresponding to the 15/7 helix were fitted by adjusting the force field. The conformation was changed, and the changes in the frequencies for the 13/6 helix and the planar zigzag were calculated using the same force field. Changes predicted for the 13/6 helix from the normal coordinate calculations are not in agreement with those actually observed at the 19°C transition. It was therefore hypothesized that the changes in the infrared and Raman spectra at this transition were due to Raman thermal defects as suggested by Brown. The potential-energy distribution was obtained for the optically active modes of the 15/7 helix, and the eigenvectors were presented for the motions of the A modes. The dispersion curve for the 15/7 helix is presented, and the coupling which occurs between the chain stretch and the CF stretching modes is discussed.
Surface-enhanced Raman scattering (SERS) from p-aminobenzoic acid (PABA) adsorbed on silver island films was investigated. PABA reacted very quickly to form p,p'-azodibenzoate when exposed to atmospheric moisture and laser light. This was evidenced by the appearance of a strong band near 1460 cm-' and a strong doublet near 1150 cm-' that were characteristic of the azodibenzoate. Exposure to a drier environment such as in a desiccator or a vacuum inhibited the reaction. It was concluded that the reaction of PABA to form the azodibenzoate involved two steps, the first being the hydrolysis of the amine and the second dimerization during exposure to laser light.
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