J.B. Hasted

Far-infrared absorption in liquid water

Abstract The results of new measurements of the far-infrared optical constants of liquid water out to 4 cm −1 at 293 K are presented. These, together with previously published submillimetre wavelength measurements, are analysed to show that it is possible to fit the continuous far-infrared-to-microwave absorption spectrum to classical polar-molecule relaxation theory with added contributions from Gaussian oscillators close to 200 and 50 cm −1 . Both of these oscillators have been observed in Raman studies. The 200 cm −1 band is well characterised in infrared measurements, but the present work represents the first unambiguous identification of the 50 cm −1 band in infrared observations.

Submillimetre wave measurements of optical constants of water at various temperatures

Abstract A polarization interferometer employing free standing wire grid polarizer and beamsplitter and reflection dispersive Fourier transform spectrometry are used to determine the optical constants of water in the region 5–220cm −1 . The liquid cell uses a single crystal semiconductor or quartz window. The complex evaluation method first determines the optical constants of the window material and then takes into account all the interface contributions in terms of ‘complex insertion loss’ formalism and thus determines the precise values of optical constants of liquids. Power absorption coefficient and refractive index data of hyperpure silicon, and power absorption coefficient, refractive index and real and imaginary parts of complex relative permittivity data of liquid water at 4. 30 and 57°C are presented and discussed.

NEW TECHNIQUES FOR DISPERSIVE FOURIER TRANSFORM SPECTROMETRY OF LIQUIDS

Abstract Dispersive Fourier transform spectrometry (DFTS) techniques are described for measuring the optical constants of liquids. Free standing wire grid polarizing and melinex beam splitters are used to cover a wide frequency range and link low and high frequency FTS data with microwave and mid infrared data respectively. Both power absorption coefficient α and refractive index n are computed as continuous functions of frequency from the same dispersive measurements and good agreement has been achieved with the power absorption coefficient spectra obtained using conventional FTS. The use of windowed liquid cells enables amplitude reflection measurements to be carried out and this not only solves the liquid vapour problem, but also permits a very thin layer (10 μm) of absorbing liquid to be used. Data are presented and discussed for water, aliphatic alcohols, halobenzenes and halogen-substituted methanes.

Absorption bands in liquid chloroform and bromoform

Abstract The optical constants of liquid chloroform and bromoform have been measured at 20°C by dispersive Fourier transform spectroscopy in the wavenumber range 20–350 cm −1 .

Resonant scattering of slow electrons from benzene and substituted benzene molecules

22 resonances in benzene and substituted benzenes have been detected in the energy range 0.5-11 eV by electron transmission. The lowest benzene resonance splits into two when the ring is perturbed by substitution.

The measurement of the refraction spectrum of a lossy liquid in the far infrared region

Abstract Dispersive Fourier transform spectrometry for the determination of the refraction spectrum of a lossy liquid is described. The principle of a first order subtraction procedure and full details of how to use it with sampled interferograms are given. The new results are compared with the results obtained using well established editing techniques and laser measurements.

Mass-spectrometric monitoring of ions in plasmas and swarms

Abstract An ion monitoring system consists of an orifice in a metal foil, an accelerating lens, a mass spectrometer and a detector. The purpose of the system is to produce an ion count which is proportional to the density of the ion species near the orifice, which is inserted into a plasma. Because this is difficult to verify experimentally, one must rely on an understanding of the theory of ion extraction through an orifice, of the ion optics, and of the mass spectrometer efficiency. These will be considered both in the electrical discharge regime and in the higher pressure flame regime. Design features of mass-spectrometric systems for sampling will also be considered. In the discharge plasma regime it is possible to operate in such a way that the ion count is proportional to the ion density, but the proportionality constant is not known accurately. The orifice plate is treated as a Langmuir probe and electron and ion currents to it can be calculated. Consideration must be given to the biasing of the orifice with respect to the plasma potential and to the role played by the plasma sheath in ion optics. Sampling of both positive and negative ions is considered. In the convective, or flame regime the dominant effect is one of cooling by expansion of the gas flowing through the orifice. Ion populations freeze at a temperature much lower than that of the flame, and collisions occur during the sampling process. Although the sampled ion populations are not characteristic of those existing in the flame, valuable information can still be obtained.

Electron scattering by water and alcohol molecules

Abstract Broad resonances in electron scattering by H2O, aliphatic alcohols and phenol are reported.

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.