Yvonne D. West

Infrared predissociation spectrum of the H3+ ion. II

The infrared predissociation spectrum of the H3+ ion has attracted considerable attention; theoretical models have been developed which account for many of the observed features and which make further predictions. This paper describes the results of experiments designed to test these predictions. The spectrum is recorded by bringing a mass‐selected H3+ ion beam into parallel or antiparallel coincidence with a cw carbon dioxide infrared laser beam. In the earlier work, 27 000 lines were observed over the range 874–1094 cm−1, each line being recorded by detecting H+ fragment ions produced by predissociation. The spectrum varied according to the H+ kinetic energy window selected, and it was proved that many of the lines arise from metastable states of H3+ lying above the H2+H+ dissociation limit. The spectrum showed no immediately recognizable pattern, but low resolution convolutions revealed the existence of a coarse‐grained structure of four main peaks. The isotopic species H2D+ and D2H+ showed similarly c...

A Fourier-transform Raman study of the strain-induced crystallization and cold crystallization of natural rubber

Abstract The Fourier-transform Raman spectrum of natural rubber is presented as a function of time of cold soaking at −25°C and of strain with respect to laser polarization. Under both sets of conditions, changes occur in the spectra that can be attributed to crystallization. Difference spectra showing only those bands due to crystallization (i.e. spectra of crystalline natural rubber) are presented, which allows the crystallization process to be discussed with respect to the conditions under which crystallites are formed. A combination of Fourier-transform Raman and Fourier-transform infra-red depolarization spectra has been used to deduce preliminary assignments for some of the vibrational bands of natural rubber.

Quantitative FT Raman analysis of two component systems

Abstract The ability to obtain quantitative information simply from Raman spectra is a subject of considerable interest. This capability exists, does not require sophisticated computer packages and is demonstrated for a mixture of cyclohexane and toluene by two independent methods. These, respectively, require the use of an external standard and the application of a linear least squares fit method to generate the observed spectrum from the pure components. Whilst these techniques avoid contamination of the analyte by the addition of an internal standard, they have, furthermore, been shown to give accurate, reproducible results.

Use of the FT Raman spectrum of Na2MoO4 to study sample heating by the laser

The difference in the FT Raman spectrum of sodium molybdate when it undergoes a crystal transition at about 112°C is used to qualitatively study laser heating effects. Relatively lower laser powers (125 mW) are able to raise the sample temperature by 40°C. Furthermore, large temperature gradients across the sample have been observed.

Microwave electronic spectroscopy, electric field dissociation and photofragmentation of the H2 + ion

Three Microwave electronic transitions in the H+2 molecular ion have been observed between the 1sσg ground state and the long-range minimum of the first excited 2pσu state. Electric field dissociation is used as an indirect method for detecting the transitions. Calculations of electric field dissociation are presented in which the rotation of the molecule is included, allowing predictions of the strengths of the electric field required to dissociate particular vibration–rotation levels in the 1sσg state. The 2pσu(v= 0, N= 2)–1sσg(v= 19, N= 1) transition was also observed using microwave photodissociation and calculations of the photodissociation cross-sections are given. An unexpected splitting was observed in two of the transitions and is interpreted in terms of g/u symmetry breaking caused by the proton Fermi contact interaction.

Spectroscopy of HD+ in high angular momentum states

Abstract We present measurements and calculations of infrared transitions between highly rotationally excited states of HD+. Some of the states involved are rotationally quasibound levels lying up to 2300 cm−1 above the lowest dissociation limit, H++D(1s). The transitions to quasibound levels were located using new ab initio artificial channels scattering theory calculations, and recorded by monitoring the fragments produced by rotational predissociation through the centrifugal barrier. The bound to bound transitions were recorded by monitoring fragments produced by photodissociation. Experimental measurements of absolute transition wavenumbers are found to be in excellent agreement with the theoretical predictions. Predissociation linewidths were also measured and are compared with theoretical calculations.

Near-dissociation microwave spectra of rare-gas diatomic ions

Abstract We have oberved microwave spectra of the inert gas diatomic ions He+2, HeAr+, HeAr+ and NeAr+. The spectra arise from transitions between levels which are within a few cm−1 of the lowest dissociation limit. We use mass-selected ion beams which pass first through a waveguide cell, and then through an electric field lens in which selective fragmentation of weakly bound levels occurs. Fragment ions produced in the lens are separated by an electrostatic analyser and detected; spectra are observed by measuring changes in the fragment ion currents. The results are discussed in terms of a theoretical model which relates the high-lying vibration—rotation levels of the diatomic ions to their atomic dissociation limits.

Advances in gallium lanthanum sulphide glass for optical fiber and devices

The advantages of gallium lanthanum sulphide (GLS) based glass over other competing glasses for active and infrared applications are evident through its low-phonon energy, high rare-earth solubility, high transition temperature and non-toxicity. However this glass often devitrifies during fibre drawing due to a small separation between the crystallisation and fibre thawing temperatures. Improving GLS fabrication technology may hold the key to achieving practical optical waveguide devices. In this paper, we describe the cunent GLS research status, methods ofimproving glass purity and our directions toward alternatives to traditional fibre technology, in particular planar channel waveguides and holey or microstructured fibres.

Comparison of the FT Raman spectra of inorganic tetrahedral ions over the temperature range 77 to 473 K

The vibrational spectra recorded over a wide temperature range (77–473 K) of a number of inorganic transition metal salts containing tetraoxyanions in both solution and crystal phases are reported. All modes in these cases are Raman active and the bands predicted by site-symmetry analysis are observed. Only bands assigned as ν3 and ν1 are found to be temperature dependent. The significance of this is discussed.

Optical amplifiers and lasers in infrared fibres

We are currently investigating two infrared glasses for active applications. Gallium lanthanum sulphide (GLS) glass is investigated as a potential host material for rare-earth doped mid-infrared fiber lasers. We have fabricated gallium lanthanum sulphide glass by melt quenching and drawn it into fibers using the rod-in-tube technique. Fluoroaluminate glasses (ALF) are being prepared in planar form by spin coating and clad waveguides have been achieved. The quality of waveguides from both these materials is gradually being improved as methods to eliminate transition metals and other impurities, understand crystallization and reduce the imperfections at the core/clad interface are developed. Although initially motivated by the demand for a practical 1310 nm amplifier, interest has now extended further into the infrared. We describe recent progress in these glasses, their properties and applications.