The Raman spectra of the two crystalline modifications of polyglycine, I and II, and of N-deuterated polyglycine II have been recorded. The results of a normal-coordinate analysis of polyglycine II and N-deuterated polyglycine II are presented along with the phonon dispersion curves of polyglycine II. Assignments are made on a number of bands not observed in the infrared. Some previous band assignments are found to be inconsistent with the Raman data.

Formulas for the transition probabilities and hence the absolute intensities of molecular vibrational spectra are obtained from a unified quantum field treatment. The theory of infrared, Raman, and hyper-Raman spectroscopy of molecular vibrations is developed by assuming these processes occur as time-ordered steps involving the creation or destruction of one quantum of vibrational energy and changes in the occupation number of one, two, or three photons, respectively. The formulas obtained by this method for ir transitions become equivalent to the earlier treatment of Jones and Simpson if the energy difference of the ground and first excited electronic energy levels are very large relative to that of the vibrational quantum. The formulas obtained for Raman transitions are very similar to those obtained by the method originated by Albrecht and developed further by Savin; we get not only the original terms of Albrecht but also the trace terms obtained by Savin. Furthermore by using third-order time-dependent equations from the start we avoid many of the difficulties of the earlier treatments; our equations predict different conditions for the resonant Raman effect than do the earlier equations, and experiments are suggested for testing the new equations. The formula which we give for the absolute intensity of the hyper-Raman effect appears to be the first ever given.

Defect energy was calculated as a function of dihedral angles of the bonds in a point dislocation for sequences of conformations that resulted in motion of the dislocation along the polyethylene chain. Paths that presented low barriers to diffusive motion of the defect were found by incrementing, in a particular sequence, selected dihedral angles around two separated bonds near the opposite ends of the defect as the computer searched for the lowest energy conformation of all the other parts of the defect. Thus, the diffusion of a point dislocation provides a plausible mechanism for diffusion of the chain along its axis.

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SYNOPSISThe density profiles of polymethylmethacrylate (PMMA) thin films on silicon ( 111 ) single crystal wafers were investigated via neutron reflectivity measurements. Films were prepared by spin casting PMMA onto silicon wafers from o-xylene solution followed by annealing under vacuum at 90°C for 5 h. A -45 A thick layer at the free polymer surface was observed in the as-prepared samples that has a density about half the value of bulk PMMA. After heating above llO°C, this diffuse layer disappeared and the thin film density profile was transformed to one with a sharp free polymer surface. This transition was found to be irreversible.