1,037 research outputs found
Recent advances in experimental techniques to probe fast excited-state dynamics in biological molecules in the gas phase : dynamics in nucleotides, amino acids and beyond
In many chemical reactions, an activation barrier must be overcome before a chemical transformation can occur. As such, understanding the behaviour of molecules in energetically excited states is critical to understanding the chemical changes that these molecules undergo. Among the most prominent reactions for mankind to understand are chemical changes that occur in our own biological molecules. A notable example is the focus towards understanding the interaction of DNA with ultraviolet radiation and the subsequent chemical changes. However, the interaction of radiation with large biological structures is highly complex, and thus the photochemistry of these systems as a whole is poorly understood. Studying the gas-phase spectroscopy and ultrafast dynamics of the building blocks of these more complex biomolecules offers the tantalizing prospect of providing a scientifically intuitive bottom-up approach, beginning with the study of the subunits of large polymeric biomolecules and monitoring the evolution in photochemistry as the complexity of the molecules is increased. While highly attractive, one of the main challenges of this approach is in transferring large, and in many cases, thermally labile molecules into vacuum. This review discusses the recent advances in cutting-edge experimental methodologies, emerging as excellent candidates for progressing this bottom-up approach
Time-resolved velocity map imaging of methyl elimination from photoexcited anisole
To date, H-atom elimination from heteroaromatic molecules following UV excitation has been extensively studied, with the focus on key biological molecules such as chromophores of DNA bases and amino acids. Extending these studies to look at elimination of other non-hydride photoproducts is essential in creating a more complete picture of the photochemistry of these biomolecules in the gas-phase. To this effect, CH3 elimination in anisole has been studied using time resolved velocity map imaging (TR-VMI) for the first time, providing both time and energy information on the dynamics following photoexcitation at 200 nm. The extra dimension of energy afforded by these measurements has enabled us to address the role of πσ* states in the excited state dynamics of anisole as compared to the hydride counterpart (phenol), providing strong evidence to suggest that only CH3 fragments eliminated with high kinetic energy are due to direct dissociation involving a 1πσ* state. These measurements also suggest that indirect mechanisms such as statistical unimolecular decay could be contributing to the dynamics at much longer times
PLANETSYS, a Computer Program for the Steady State and Transient Thermal Analysis of a Planetary Power Transmission System: User's Manual
The material presented is structured to guide the user in the practical and correct implementation of PLANETSYS which is capable of simulating the thermomechanical performance of a multistage planetary power transmission. In this version of PLANETSYS, the user can select either SKF or NASA models in calculating lubricant film thickness and traction forces
In-situ measurements of fabrication induced strain in diamond photonic-structures using intrinsic colour centres
Diamond has established itself as an ideal material for photonics and optomechanics, due to its broad-band transparency and hardness. In addition, colour centres hosted within its lattice such as the nitrogen-vacancy (NV) centre, have become leading candidates for use in quantum information processing, and quantum sensors. The fabrication of nanoscale devices coupled to high quality NVs has been an outstanding challenge due to their sensitivity to magnetic, electric and strain fields within their local environment. In this work, we show how the NV centre’s ground state electron spin can be used as an embedded atomic-scale probe of the local strain caused by focused ion beam milling of nanoscale devices. This technique can thus be used to measure, and optimise material and device fabrication processes to allow diamond to reach its full potential
Strongly enhanced photon collection from diamond defect centres under micro-fabricated integrated solid immersion lenses
The efficiency of collecting photons from optically active defect centres in
bulk diamond is greatly reduced by refraction and reflection at the diamond-air
interface. We report on the fabrication and measurement of a geometrical
solution to the problem; integrated solid immersion lenses (SILs) etched
directly into the surface of diamond. An increase of a factor of 10 was
observed in the saturated count-rate from a single negatively charged
nitrogen-vacancy (NV-) within a 5um diameter SIL compared with NV-s under a
planar surface in the same crystal. A factor of 3 reduction in background
emission was also observed due to the reduced excitation volume with a SIL
present. Such a system is potentially scalable and easily adaptable to other
defect centres in bulk diamond.Comment: 5 Pages, 5 figures (4 subfigures) - corrected typ
Velocity Map Imaging the Scattering Plane of Gas Surface Collisions
The ability of gas-surface dynamics studies to resolve the velocity
distribution of the scattered species in the 2D sacattering plane has been
limited by technical capabilities and only a few different approaches have been
explored in recent years. In comparison, gas-phase scattering studies have been
transformed by the near ubiquitous use of velocity map imaging. We describe an
innovative means of introducing a surface within the electric field of a
typical velocity map imaging experiment. The retention of optimum velocity
mapping conditions was demonstrated by measurements of iodomethane-d3
photodissociation and SIMION calculations. To demonstrate the systems
capabilities the velocity distributions of ammonia molecules scattered from a
PTFE surface have been measured for multiple product rotational states.Comment: 8 pages, 5 figures, to be submitted to journa
Photo-dynamics of quantum emitters in aluminum nitride
Aluminum nitride is a technologically important wide bandgap semiconductor
which has been shown to host bright quantum emitters. In this paper, we probe
the photodynamics of quantum emitters in aluminum nitride using photon emission
correlations and time-resolved spectroscopy. We identify that each emitter
contains as many as 6 internal energy levels with distinct laser
power-dependent behaviors. Power-dependent shelving and de-shelving processes,
such as optically induced ionization and recombination are considered,
indicating complex optical dynamics associated with the spontaneous and
optically pumped transitions. State population dynamics simulations
qualitatively explain the temporal behaviours of the quantum emitters,
revealing that those with pump-dependent de-shelving processes can saturate at
significantly higher intensities, resulting in bright room-temperature quantum
light emission.Comment: 20 pages. 5 figures in main text, 3 in supplementary inf
- …