QUENCHING OF CHLOROPHYLL FLUORESCENCE BY NITROBENZENE

Abstract—Nitrobenzene quenching of chlorophyll fluorescence in ethanol has been investigated. Steady state relative quantum yields have been measured and fluorescence decay rates were determined using both nanosecond photon counting and picosecond pulses from a mode-locked Nd³⁺ glass laser.
The fluorescence decay is described by
1( t )= I ₀ exp (- t/τ−At^1/2 )
the form predicted for decay governed by the kinetics of the continuum model of diffusion controlled reactions. From the parameters of the fluorescence decay, the encounter distance is 5–7 A° the mutual diffusion coefficient is 0.62 × 10^--⁵ cm2s^-1± 12%.
Some of the fluorescence quenching is also attributed to static quenching by a nitrobenzene-chlorophyll, ground-state complex. The equilibrium constant for formation of this ground-state complex was determined to be 4.1 M ^-1. The combined dynamic and static quenching model allows calculation of quantum yields of fluorescence in good agreement with the experimentally determined quantum yields.     

Layer Communities in Multiplex Networks

Journal of Statistical Physics - Multiplex networks are a type of multilayer network in which entities are connected to each other via multiple types of connections. We propose a method, based on...     

Spectra of K4Ru(CN)6

Luminescence of complex ions is a general phenomenon; the number of such complexes in various electronic configurations found to show emission is increasing rapidly. For some it has been possible to assign the emission as phosphorescence or as fluorescence, for others the proper assignment is as yet not clear.     

Highly charged ions in a new era of high resolution X-ray astrophysics

X-ray astronomy and ground-based atomic physics have a long history of fruitful collaboration: Sound understanding of the underlying atomic physics is the key to reliable interpretation of the spectra from celestial sources; conversely, astronomical spectra have been used to benchmark and advance atomic physics. This interplay is about to become even more important as we enter a new era of high-resolution X-ray astrophysics with large effective collection area. Although high-resolution observations with the gratings on the Chandra and XMM-Newton observatories continue to drive new science, upcoming planned and proposed missions will open up new discovery space in the near future that is currently challenging to access: high-resolution spectroscopy on extended sources, in the Fe K band, and on short time scales. This review summarizes open questions in these areas and the design parameters for the Hitomi, XRISM, Athena, and Arcus observatories. The expected high quality of spectra taken with these observatories puts new constraints on the accuracy of atomic reference data required to take full advantage of the diagnostic potential of these spectra.     

Two new marine sediment standard reference materials (SRMs) for the determination of organic contaminants

Two new marine sediment standard reference materials (SRMs), SRM 1941b Organics in Marine Sediment and SRM 1944 New York/New Jersey Waterway Sediment, have been recently issued by the National Institute of Standards and Technology (NIST) for the determination of organic contaminants including polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyl (PCB) congeners, and chlorinated pesticides. Both sediment SRMs were analyzed using multiple analytical methods including gas chromatography/mass spectrometry (GC/MS) on columns with different selectivity, reversed-phase liquid chromatography with fluorescence detection (for PAHs only), and GC with electron capture detection (for PCBs and pesticides only). SRM 1941b has certified concentrations for 24 PAHs, 29 PCB congeners, and 7 pesticides, and SRM 1944 has certified concentrations for 24 PAHs, 29 PCB congeners, and 4 pesticides. Reference concentrations are also provided for an additional 58 (SRM 1941b) and 39 (SRM 1944) PAHs, PCB congeners, and pesticides. SRM 1944, which was collected from multiple sites within New York/New Jersey coastal waterways, has contaminant concentrations that are generally a factor of 10–20 greater than SRM 1941b, which was collected in the Baltimore (Maryland) harbor. These two SRMs represent the most extensively characterized marine sediment certified reference materials available for the determination of organic contaminants.Electronic Supplementary Material Supplementary material is available in the online version of this article at . A link in the frame on the left on that page takes you directly to the supplementary material.     

Symmetric inertial-confinement-fusion-capsule implosions in a double-z-pinch-driven hohlraum

An inertial-confinement-fusion (ICF) concept using two 60-MA Z pinches to drive a cylindrical hohlraum to 220 eV has been recently proposed. The first capsule implosions relevant to this concept have been performed at the same physical scale with a lower 20-MA current, yielding a 70+/-5 eV capsule drive. The capsule shell shape implies a polar radiation symmetry, the first high-accuracy measurement of this type in a pulsed-power-driven ICF configuration, within a factor of 1.6-4 of that required for scaling to ignition. The convergence ratio of 14-21 is to date the highest in any pulsed-power ICF system.     

Broken symmetries and pattern formation in two-frequency forced faraday waves

We exploit the approximate (broken) symmetries of time translation, time reversal, and Hamiltonian structure to obtain general scaling laws governing the process of pattern formation in weakly damped Faraday waves. Using explicit parameter symmetries we determine, for the case of two-frequency forcing, how the strength of observed three-wave interactions depends on the frequency ratio and on the relative phase of the two driving terms. These symmetry-based predictions are verified for numerically calculated coefficients, and help explain the results of recent experiments.     

A numerical method for acoustic normal modes for shear flows

The normal modes and their propagation numbers for acoustic propagation in wave guides with flow are the eigenvectors and eigenvalues of a boundary value problem for a non-standard Sturm-Liouville problem. It is non-standard because it depends non-linearly on the eigenvalue parameter. (In the classical problem for ducts with no flow, the problem depends linearly on the eigenvalue parameter.) In this paper a method is presented for the fast numerical solution of this problem. It is a generalization of a method that was developed for the classical problem. A finite difference method is employed that combines well known numerical techniques and a generalization of the Sturm sequence method to solve the resulting algebraic eigenvalue problem. Then a modified Richardson extrapolation method is used that dramatically increases the accuracy of the computed eigenvalues. The method is then applied to two problems. They correspond to acoustic propagation in the ocean in the presence of a current, and to acoustic propagation in shear layers over flat plates.     

Excited states in the photochemistry of chromium(III) complexes

Experimental data for chromium(III) complex ions on the spectroscopic properties, photoreactions, and intermolecular energy transfer are analyzed in terms of the primary photophysical and photochemical processes. It is suggested that the lowest excited quartet state,⁴T_2g inO _h symmetry, is the immediate precursor to photoaquation and that the lowest doublet state,²E, is substitution inert except via the⁴ T _2g state reached by back intersystem crossing.

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Zusammenfassung Experimentelle Daten von Chrom-(III)-Komplex-Ionen in bezug auf spektroskopische Eigenschaften, Photoreaktionen und intermolekularen Energieübertragung wurden mit dem Begriffssystem der photophysikalischen und photochemischen Primärprozesse analysiert. Und zwar wird vorgeschlagen, daß der tiefste angeregte Quartettzustand,⁴ T _2g inO _h -Symmetrie, der unmittelbare Vorläufer der Photoaquatisierung ist und daß der tiefste Doublettzustand,²E, inert gegenüber Substitutionen ist, außer über den⁴ T _2g Zustand, wenn er durch Re-intersystem crossing erreicht wird.

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Dedicated to the memory of Professor Hans-Ludwig Schläfer.