Elisabeth A. Nicol

The far infra-red spectrum of crystalline polytetrafluoroethylene

Abstract The far infra-red spectrum of highly crystalline polytetrafluoroethylene has been shown to contain a new band near 33cm−1, the band at 55cm−1 has been shown to be a close doublet and two further bands at 291 and 308cm−1 have been observed. These results strongly support the conclusions of Boerio and Koenig from Raman observations that the unit cell contains at least two molecular segments.

Temperature effects and the observation of the B2u lattice mode in the far infrared absorption spectrum of polyethylene

Abstract Using high precision radiometry in conjuction with a Michelson far infrared spectrometer the B 2u lattice mode of polyethylene has been observed at both room and liquid-nitrogen temperatures. The continuum absorption of polyethylene in the far infrared has been shown to be temperature dependent from whick it is concluded that difference type multiphonon bands make a considerable contribution.

The FIR optical constants of the polymer TPX

Abstract The optical constants of the polymer TPX have been determined between 30 and 420 cm−1 at ambient temperature by the technique of dispersive Fourier transform spectroscopy. The results are compared with previous measurements.

On the vibrational assignment problem for polytetrafluoroethylene: 1. The far infra-red spectrum

Studies of the polarized far infra-red spectra of drawn specimens of polytetrafluoroethylene (PTFE) and of the spectrum of the oligomer C14F30 both at room and liquid nitrogen temperatures have given results which strongly confirm the general form of recently published dispersion diagrams. However the absolute values of band intensities and their variation with specimen morphology suggest that some minor changes to the optical intersections are necessary. Intensity arguments also strongly indicate that the labelling, adopted by most recent workers, for the branches B6 and B7 should be interchanged.

Temperature effects and the observation of lattice bands in the far infrared spectrum of polytetrafluorethylene

Abstract Four discrete bands have been observed in the region 40–90 cm−1 for polytetrafluorethylene samples at low temperatures. These are assigned as lattice bands and the observation confirms the deduction from earlier Raman studies that the unit cell contains more than one molecular segment. Continuum absorption in the far infrared for polytetrafluorethylene has been shown to be a function of crystallinity and temperature.

FIR spectra of saccharides and polysaccharides

Abstract Measurements of the FIR absorption spectra of polysaccharides and their constituent monoand disaccharides have been made between 30 and 650 cm −1 , using FTS. Some of the structure of the saccharides is found to show up in the polymers.

FIR spectra of amino acids and related molecules

Abstract FIR spectra of the 22 naturally-occurring L-amino acids, together with those of related molecules sodium acetate, benzoic acid, dinitrobenzoic acid, urea and hydroquinone, have been measured in the spectral range 30–650 cm −1 , by means of FTS. Some interpretation is made with the aid of existing normal mode analyses of glycine, l -alanine and dl -serine.

A far infra-red study of conformational disorder in PTFE

Abstract The examination of the 250–350 cm −1 region of the infra-red spectrum of polytetrafluoroethylene (PTFE) has been extended by studies of thermally degraded and sintered material. We conclude that a band at 277 cm −1 does not arise from a true mode of the crystal but has its origin in regions where the chain has a bent conformation. Our previous speculation that bands at 292 cm −1 and 312 ∗ cm −1 (Raman active only, for the isolated chain) acquire their weak activity in the infra-red through conformational disorder is confirmed. It is likely that the conformational disorder in question arises from chain folding in the polymer crystal.

Vibrational spectrum, assignment and molecular symmetry of phenyl isocyanate in the liquid phase

Abstract Infrared (30–4000 cm−1) and laser-Raman (100–3100 cm−1) spectra are reported for phenyl isocyanate in the liquid phase and far infrared data are given for the polycrystalline phase. The literature assignment is not compatible with the new data and a complete revision is given for an assumed C2υ symmetry. However, microwave spectroscopy indicates that the symmetry in the vapour phase is no higher than Cs and the liquid state spectra are much better assigned under the supposition that in this phase also the CNC angle is less than 180°.

The removal of detector port radiation effects in power transmission or reflection Fourier transform spectroscopy

Abstract In interferometers which employ internal modulation schemes, radiation from the detector port of the instrument can contribute to the detected interferometrically modulated signal. This can cause the spectrum measured in a power transmission or reflection experiment to be significantly different from the corresponding real spectrum of the specimen. A measurement procedure that allows the effect of this detector port radiation to be removed is described and demonstrated.