Brian J. Orr

Wavelength modulation spectroscopy (WMS), using a 1654 nm diode laser and an annular polygon-reflector multipass optical cell, has been developed for quantitative measurement of enteric emissions of methane (CH ₄ ) from ruminant livestock at atmospheric pressure. WMS is molecule-specific and able to detect sub-parts-per-million concentrations of CH ₄ in ambient air. Periodic bursts of CH ₄ from a pulsed solenoid valve enable laboratory-based simulation of such animal emissions, demonstrating the feasibility of using WMS to time-resolve individual simulated eructations of CH ₄ in cattle breath and providing the basis for subsequent field-based instruments designed to measure CH ₄ emissions from livestock.

Professor A. David Buckingham CBE FRS FAA made fundamental theoretical and experimental contributions to the understanding of optical, electric and magnetic properties of molecules. Born in Australia, he was an undergraduate at the University of Sydney and took his PhD at the University of Cambridge, UK. He moved to Oxford in 1955 and then in 1965 became Professor of Theoretical Chemistry at the University of Bristol. Finally, he moved back to Cambridge in 1969 for twenty-eight years as Professor of Chemistry and head of a distinguished Department of Theoretical Chemistry. A man of broad interests and achievements, he played first class cricket in the 1950s.

Various forms of time-resolved optical double-resonance spectroscopy facilitate rotationally resolved measurements of collision-induced intramolecular vibration-to-vibration (V-V) energy-transfer processes, which take a gas-phase polyatomic molecule from one distinct rovibrational energy level to another. Of longstanding mechanistic interest are questions concerning the extent to which such V-V energy transfer (ET) may be influenced by intramolecular perturbations - notably Fermi resonance (and other anharmonic mixing effects) and Coriolis coupling - within polyatomic molecular rovibrational manifolds of interest. It is evident that quantum-mechanical interference effects can arise, either inhibiting or enhancing the probability of collision-induced ET in perturbed rovibrational manifolds of certain small gas-phase polyatomic molecules, notably CO2, D2CO and C2H2. This article focuses on a blend of high-resolution rovibrational spectroscopy (characterising initial and final molecular levels and their intramolecular perturbations) and collision dynamics (with colliding molecules defined in terms of isolated-molecule spectroscopic basis states). It aims to offer fresh insights and to consider some apparent mechanistic anomalies (e.g. collision-induced quasi-continuous background effects in the 4 nu(CH) rovibrational manifold of C2H2). Various reported experiments and related theoretical treatments are critically re-examined, in order to pose and address mechanistic questions some of which still challenge detailed understanding. [GRAPHICS] .

A tunable, narrowband laser system, developed for high-resolution ultraviolet spectroscopy of atoms and molecules and previously applied to two-photon excitation of rare-gas atoms, now offers prospects for new measurements of atmospheric molecules such as oxygen.

Mass-selective sub-Doppler two-photon excitation (TPE) spectroscopy is employed to resolve isotopic contributions for transitions to high-energy Rydberg levels of xenon in an atomic beam, using narrowband pulses of coherent ultraviolet light at 205–213 nm generated by nonlinear-optical conversion processes. Previous research (Kono et al 2013 J. Phys. B: At. Mol. Opt. Phys. 46 35401), has determined isotope energy shifts and hyperfine structure for 33 high-energy Rydberg levels of gas-phase xenon and accessed Rydberg levels at TPE energies in the range of 94 100–97 300 cm⁻¹ with unprecedented spectroscopic resolution. The new isotopic-mass-resolved results were obtained by adding a pulsed free-jet atomic-beam source and a mass-selective time-of-flight detector to the apparatus in order to discern individual xenon isotopes and extract previously unresolved spectroscopic information. Resulting isotope energy shifts and hyperfine-coupling parameters are examined with regard to trends in principal quantum number n and in atomic angular-momentum quantum numbers, together with empirical and theoretical precedents for such trends.

Passive phase-conjugation enables precise fiber-optical transfer of radio-frequency reference signals over long distances, yielding high long-term stability for radio-astronomy and remote-sensing applications without active path-length stabilization.

Single-mode optical fibers can be used to couple remotely located open-path ringdown cavities to a single central control module. This enables laser-spectroscopic sensing of atmospheric species at trace levels in agricultural and environmental media.

Optical-fiber networks, compensated for path-length fluctuations, enable long-distance dissemination of a radio-frequency signal for precise spectroscopic calibration at remote sites in environmental, industrial and energy-monitoring applications.