I. H. Munro

Reflection absorption infrared spectroscopy at the Daresbury SRS

The high brilliance of modern synchrotron radiation sources results in a significant intensity advantage over conventional sources in the far infrared region of the spectrum. For applications with inherently low etendue, such as reflection absorption infrared spectroscopy (RAIRS) of surfaces, this advantage extends into the mid‐infrared (IR) region, to 1000 cm−1 or higher. The spectroscopic region between 100 and 1000 cm−1 is of particular interest in surface science since it includes the vibrational modes of the majority of direct bonds between the surface and adsorbate, but the low intensity of conventional sources renders investigations of this region difficult. In this paper, we discuss the design criteria of the new Daresbury infrared beamline.

Photophysical properties of DPH derivatives

Abstract The absorption spectra, fluorescence emission spectra, quantum yields and fluorescence lifetimes have been measured for a range of DPH derivatives. Difference in the photophysical properties as compared with those of DPH are noted and discussed.

Luminescence quenching as a probe for the local density of electronic excitations in insulators

Abstract Luminineence quenching which originates from the interaction of closely spaced electronic excitations (EEs: electrons, core- and valence-band holes, excitons, etc.) is considered. ‘Reactions’ between them at a distance shorter than that of dipole-dipole interaction are discussed. Creation of regions with high local density of EEs by VUV and XUV photons is demonstrated. Features of this type of quenching specific for different regions of excitation and different crystals are illustrated by experimental examples.

The use of site-directed mutagenesis and time-resolved fluorescence spectroscopy to assign the fluorescence contributions of individual tryptophan residues in Bacillus stearothermophilus lactate dehydrogenase

Site-directed mutagenesis has been used to generate two mutant Bacillus stearothermophilus lactate dehydrogenases: in one, Trp-150 has been replaced with a tyrosine residue and, in the other, both Trp-150 and -80 are replaced with tyrosines. Both enzymes are fully catalytically active and their affinities for substrates and coenzymes, and thermal stabilities are very similar to those of the native enzyme. Time-resolved fluorescence measurements using a synchrotron source have shown that all three tryptophans in the native enzyme fluoresce. By comparing the mutant and native enzymes it was possible, for the first time, to assign, unambiguously, lifetimes to the individual tryptophans: Trp-203 (7.4 ns), Trp-80 (2.35 ns) and Trp-150 (less than 0.3 ns). Trp-203 is responsible for 75-80% of the steady-state fluorescence emission, Trp-80 for 20%, and Trp-150 for less than 2%.

Fast luminescence of cerium doped lanthanum fluoride

Abstract Spectral and decay time characteristics of the VUV and X-ray excited luminescence of LaF3Ce crystals have been measured. A mechanism for the fast (2 ns) component of luminescence is proposed, namely emission from Ce3+∗F0 centers, formed as the result of nonradiative transfer of energy from transitions between the upper core and valence bands.

Synchrotron radiation as a light source in confocal microscopy

The optical properties of a confocal scanning microscope that was designed to utilize a synchrotron as light source are presented. The usable spectral range is from 200 nm up to 700 nm. Using 325‐nm laser light, it is shown that the lateral resolution is about 125 nm, and the axial resolution better than 250 nm. After transport of the microscope from Utrecht to the Daresbury Synchrotron Source, 200‐nm excitation can be applied, and the lateral resolution will drop to below 100 nm.

Ion-recombination luminescence in alkanes excited by synchrotron radiation in the range 10–40 eV

Abstract Time-resolved single-photon counting has been used to study ion-recombination luminescence in squalane solutions of paraterphenyl. The synchrotron storage ring at Daresbury provided excitation pulses in the photon energy range 10–40 eV. Changes in luminescence pulse shape and in the effect of applied magnetic field were observed. The results are related to the behaviour of multi-ion pair spurs produced by fast electrons or beta-particles.

Luminescence of DNA excited in the vacuum ultraviolet

Abstract Pulsed vacuum ultraviolet radiation has been used to excite DNA in the energy range 12 to 30 eV. Time-resolved single-photon counting shows non-exponential luminescence decays over some hundreds of nanoseconds: the application of a magnetic field demonstrates the role of radical-ion recombination and, at higher energies, of fission into two triplet species.

Micro-Volume Time-Resolved Fluorescence Spectroscopy Using a Confocal Synchrotron Radiation Microscope

The confocal microscope SYCLOPS (SYCLOPS is not an acronym although the first syllable is derived from its main light source, a synchrotron radiation source) at the Daresbury Science and Engineering Research Council (SERC) Laboratory, U.K., has been designed to facilitate fluorescence decay measurements on microscopic volume elements. SYCLOPS utilizes the Daresbury Synchrotron Radiation Source (SRS) as a pulsed light source. Visible or UV excitation light is selected from the white synchrotron radiation spectrum with a bandpass filter matching the absorption band of the fluorophores. Decay curves of fluorescence intensity emitted by a pre-selected micro-volume in the sample can be acquired with standard time-correlated single-photon counting techniques. The fluorescence intensity was collected from a confocal spot with a volume of 3 μm3. The first lifetime measurements done with the instrument were carried out on a coumestrol l]benzopyran-6-one) solution and on different cellular compartments of living cells incubated with coumestrol.

Radiative core-valence transitions in CsMgCl3 and CsSrCl3

Abstract In this work the spectra and decay times of the intrinsic luminescence of CsMgCl3 and CsSrCl3 have been studied. Measurements were undertaken using a pulsed X-ray source (at Saint-Petersburg State Technical University) and SRS at Daresbury Laboratory. The results enable us to relate the short-lived luminescence in the chlorides studied to their radiative core-valence transitions. In addition, the energy band parameters of the crystals were deduced.