Positronium and quantum electrodynamics

1982 ◽  
Vol 60 (4) ◽  
pp. 543-550 ◽  
Author(s):  
D. W. Gidley
Keyword(s):  
Fine Structure ◽  
Excited State ◽  
Hyperfine Structure ◽  
Ground State ◽  
Quantum Electrodynamics ◽  
Experimental Tests ◽  
Decay Rates ◽  
Experimental Techniques

Experimental tests of quantum electrodynamics using positronium are reviewed. These tests include measurements of the ground state hyperfine structure, excited state fine structure, and the annihilation decay rates of positronium. Emphasis is given to describing the present experimental techniques, comparing the most recent results with theory, and summarizing possible future improvements in the measurements.

Analyse Rotationnelle de la Bande (0,0) du Système Orange de ScO

1972 ◽  
Vol 50 (4) ◽  
pp. 395-403 ◽  
Author(s):  
R. Stringat ◽  
C. Athénour ◽  
J. L. Féménias
Keyword(s):  
Excited State ◽  
Hyperfine Interaction ◽  
Hyperfine Structure ◽  
Liquid Nitrogen ◽  
Hollow Cathode ◽  
Ground State ◽  
Type B ◽  
Hollow Cathode Lamp ◽  
Magnetic Hyperfine Interaction ◽  
Coupling Case

The orange system of ScO has been reanalyzed as a 2Π → 2Σ transition. We have observed all the branches which are compatible with the selection rules ΔJ = 0, ± 1. We have not detected the hyperfine structure in the excited state, the coupling case being therefore aβ. The magnetic hyperfine interaction inducing the ground state doubling is the only one which appears; it has been analyzed by other authors who have shown that the coupling case for this state is of the type bβS.The use of an alloy hollow-cathode lamp, cooled with liquid nitrogen, has enabled us to improve the frequency measurements. The values of the constants have been obtained by a method by which, working directly with the Hamiltonian, the introduction of each parameter can be justified. The study of the Λ doubling in 2Π3/2 and 2Π1/2 levels leads us to values of ξ and η very close to those predicted for a pure precession case.

Photoneutron cross sections in 7Li

1977 ◽  
Vol 55 (5) ◽  
pp. 428-433 ◽  
Author(s):  
H. Ferdinande ◽  
N. K. Sherman ◽  
K. H. Lokan ◽  
C. K. Ross
Keyword(s):  
Fine Structure ◽  
Excited State ◽  
Cross Section ◽  
Cross Sections ◽  
Ground State ◽  
Reasonable Agreement ◽  
Branching Ratio ◽  
Energy Spectra ◽  
Average Value ◽  
First Excited State

Photoneutron energy spectra from 7Li have been measured by time-of-flight methods, for bremsstrahlung end-point energies increasing in 2 MeV steps from 13 to 25 MeV. The ground-state and approximate first-excited-state differential cross sections at 90° have been obtained from 8.5 to 23 MeV. No pronounced fine structure has been observed. The measured branching ratio to the first excited state falls from an average value of 0.70 between 10.3 and 14.5 MeV to an average of 0.29 between 14.5 and 18 MeV, and rises again to an average of 0.38 between 18 and 23 MeV. This behaviour can be explained by a crude theoretical model in which 1p → 2s and 1p → 1d single particle transitions dominate below 18 MeV. The calculation predicts a branching ratio of 0.50 near threshold, falling to 0.23 at higher energies, in reasonable agreement with the experiment. The integrated value of the ground-state cross section up to 23 MeV is about (38.7 ± 3.9) MeV mb, while that for the first excited state is about (17.2 ± 3.4) MeV mb. Together they account for 39% of the exchange-augmented dipole sum of 7Li.

scholarly journals Some possibilities for laboratory searches for variations of fundamental constants

2000 ◽  
Vol 78 (7) ◽  
pp. 639-678 ◽  
Author(s):  
S G Karshenboim
Keyword(s):  
Fine Structure ◽  
Hyperfine Structure ◽  
Magnetic Moment ◽  
Ground State ◽  
Fundamental Constants ◽  
Time And Space ◽  
Advantages And Disadvantages ◽  
Hydrogen Deuterium ◽  
Small Magnetic Moment

We consider different options for the search for possible variations of the fundamental constants. We give a brief overview of the results obtained with several methods. We discuss their advantages and disadvantages with respect to simultaneous variations of all constants in both time and space in the range 108–1010 years. We also suggest a few possibilities for the laboratory search. Particularly, we propose some experiments with the hyperfine structure of hydrogen, deuterium, and ytterbium–171 and of some atoms with a small magnetic moment. Other suggestions are for some measurements of the fine structure associated with the ground state. Special attention is paid to the interpretation of the hfs measurements in terms of variations of the fundamental constants. PACS No.: 31.30G

Fine structure in the photoneutron spectra from praseodymium-141 and lead

1970 ◽  
Vol 48 (8) ◽  
pp. 950-953 ◽  
Author(s):  
K. G. McNeill ◽  
J. W. Jury ◽  
J. S. Hewitt
Keyword(s):  
Fine Structure ◽  
Excited State ◽  
Energy Spectrum ◽  
Cross Section ◽  
Ground State ◽  
Giant Dipole Resonance ◽  
Daughter Nucleus ◽  
State Transitions ◽  
Dipole Resonance ◽  
Section Curve

Careful measurements of the energy spectrum of photoneutrons ejected from praseodymium and from natural lead show that there are peaks on top of the expected smooth spectrum. Comparison with the recent cross-section studies, which indicate structure on the giant dipole resonance for these nuclei, shows agreement between the energies of the peaks found in the present work and the energies En = E−Qi where E corresponds to a peak in the cross-section curve and Qi is the threshold for producing a given state in the daughter nucleus. Only ground state transitions (for Pr) or ground state and the first two excited state transitions (for Pb) need be invoked.

Influence of excited-state hyperfine structure on ground-state coherence

1999 ◽  
Vol 61 (1) ◽  
Author(s):  
A. Nagel ◽  
C. Affolderbach ◽  
S. Knappe ◽  
R. Wynands
Keyword(s):  
Excited State ◽  
Hyperfine Structure ◽  
Ground State

Renilla Bioluminescence: A Morphologic Approach to the Location of Photocytes

1974 ◽  
Vol 32 ◽  
pp. 208-209
Author(s):  
Ben O. Spurlock ◽  
Milton J. Cormier
Keyword(s):  
Excited State ◽  
Ground State ◽  
Molecular Basis ◽  
Light Emission ◽  
Chemical Basis ◽  
Electronic Excited State ◽  
Colonial Form ◽  
The Common ◽  
Eighteenth And Nineteenth Centuries ◽  
Catalyzed Oxidation

The phenomenon of bioluminescence has fascinated layman and scientist alike for many centuries. During the eighteenth and nineteenth centuries a number of observations were reported on the physiology of bioluminescence in Renilla, the common sea pansy. More recently biochemists have directed their attention to the molecular basis of luminosity in this colonial form. These studies have centered primarily on defining the chemical basis for bioluminescence and its control. It is now established that bioluminescence in Renilla arises due to the luciferase-catalyzed oxidation of luciferin. This results in the creation of a product (oxyluciferin) in an electronic excited state. The transition of oxyluciferin from its excited state to the ground state leads to light emission.

Ground State and Excited State H-Atom Temperatures in a Microwave Plasma Diamond Deposition Reactor

1996 ◽  
Vol 6 (9) ◽  
pp. 1167-1180 ◽  
Author(s):  
A. Gicquel ◽  
M. Chenevier ◽  
Y. Breton ◽  
M. Petiau ◽  
J. P. Booth ◽  
...  
Keyword(s):  
Excited State ◽  
Ground State ◽  
Microwave Plasma ◽  
Diamond Deposition

Spin-Forbidden Excitation Enables Infrared Photoredox Catalysis

2020 ◽  
Author(s):  
Tomislav Rovis ◽  
Benjamin D. Ravetz ◽  
Nicholas E. S. Tay ◽  
Candice Joe ◽  
Melda Sezen-Edmonds ◽  
...  
Keyword(s):  
Excited State ◽  
Ground State ◽  
Intersystem Crossing ◽  
Photoredox Catalysis ◽  
Infrared Irradiation ◽  
Triplet Excitation ◽  
New Family ◽  
Ir Light

We describe a new family of catalysts that undergo direct ground state singlet to excited state triplet excitation with IR light, leading to photoredox catalysis without the energy waste associated with intersystem crossing. The finding allows a mole scale reaction in batch using infrared irradiation.

Excited-State Dynamics in the RNA Nucleotide Uridine 5’-Monophosphate Investigated by Femtosecond Broadband Transient Absorption Spectroscopy

2019 ◽  
Author(s):  
Matthew M. Brister ◽  
Carlos Crespo-Hernández
Keyword(s):  
Excited State ◽  
Excited States ◽  
Ground State ◽  
Transient Absorption ◽  
Electronic Energy ◽  
Transient Absorption Spectroscopy ◽  
Electronic Relaxation ◽  
Vibrationally Excited ◽  
Excited State Dynamics ◽  
Π State

<p></p><p> Damage to RNA from ultraviolet radiation induce chemical modifications to the nucleobases. Unraveling the excited states involved in these reactions is essential, but investigations aimed at understanding the electronic-energy relaxation pathways of the RNA nucleotide uridine 5’-monophosphate (UMP) have not received enough attention. In this Letter, the excited-state dynamics of UMP is investigated in aqueous solution. Excitation at 267 nm results in a trifurcation event that leads to the simultaneous population of the vibrationally-excited ground state, a longlived <sup>1</sup>n<sub>O</sub>π* state, and a receiver triplet state within 200 fs. The receiver state internally convert to the long-lived <sup>3</sup>ππ* state in an ultrafast time scale. The results elucidate the electronic relaxation pathways and clarify earlier transient absorption experiments performed for uracil derivatives in solution. This mechanistic information is important because long-lived nπ* and ππ* excited states of both singlet and triplet multiplicities are thought to lead to the formation of harmful photoproducts.</p><p></p>

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