Excitation Processes in Cometary Comae

1987 ◽  
pp. 455-459
Author(s):  
P. D. Singh
Keyword(s):  
Excitation Processes ◽  
Cometary Comae

scholarly journals Excitation Processes in Cometary Comae

1987 ◽  
Vol 120 ◽  
pp. 455-459
Author(s):  
P. D. Singh
Keyword(s):  
Electron Recombination ◽  
Recombination Processes ◽  
Excitation Processes ◽  
Cometary Comae

Excitations of cometary NH and S2 molecules are discussed. Photodissociation and dissociative electron recombination processes may be sources of meta-stable nitrogen (2Po, 2Do) atoms in comets.

scholarly journals High-Resolution Optical and Infrared Observations of Molecules in Comets

2000 ◽  
Vol 197 ◽  
pp. 471-480 ◽  
Author(s):  
S. J. Kim ◽  
Y. C. Minh ◽  
S. Hyung ◽  
Y. H. Kim
Keyword(s):  
High Resolution ◽  
Solar Nebula ◽  
Solar System Formation ◽  
Cometary Nuclei ◽  
Infrared Observations ◽  
Spectroscopic Observations ◽  
Radio Range ◽  
Excitation Processes ◽  
Molecular Abundances ◽  
Cometary Comae

Molecules in cometary nuclei are considered to contain information on the constituents in the proto-solar nebula at the time of solar system formation. The composition of cometary nuclei has been indirectly derived from spectroscopic observations of molecules in comae. Ambitious space missions to cometary nuclei for landing and sample return are planned to be realized in 4–7 years. Until then, spectroscopic observations remain a powerful way to remotely investigate molecules and ions in cometary comae. Recent bright comets such as Hale-Bopp (C/1995 O1) and Hyakutake (C/1996 B2) have provided detections of new molecules in comae. Observational results from high-resolution optical and infrared spectroscopy of Hale-Bopp, Hyakutake and recent comets, are presented. In particular, symmetric molecules, which have zero electric dipole moment and are therefore not observable in the radio range, have been detected in several recent comets by infrared observations. The new data can also be used to derive accurate abundances of known molecular species. We present the time-dependent excitation processes of the bands of these molecules and discuss the influence of the fluorescence calculations on the derivations of molecular abundances in comets.

Valence electron energy loss spectroscopy in reflection geometry

1989 ◽  
Vol 47 ◽  
pp. 378-379
Author(s):  
J. Liu ◽  
J. M. Cowley
Keyword(s):  
Energy Loss ◽  
Valence Electron ◽  
Interband Transition ◽  
Specular Reflection ◽  
Three Dimensional ◽  
Electron Excitation ◽  
Transmission Electron ◽  
Yield Information ◽  
Valence Bands ◽  
Excitation Processes

The low energy loss region of a EELS spectrum carries information about the valence electron excitation processes (e.g., collective excitations for free electron like materials and interband transitions for insulators). The relative intensities and the positions of the interband transition energy loss peaks observed in EELS spectra are determined by the joint density of states (DOS) of the initial and final states of the excitation processes. Thus it is expected that EELS in reflection mode could yield information about the perturbation of the DOS of the conduction and valence bands of the bulk crystals caused by the termination of the three dimensional periodicity at the crystal surfaces. The experiments were performed in a Philipps 400T transmission electron microscope operated at 120 kV. The reflection EELS spectra were obtained by a Gatan 607 EELS spectrometer together with a Tracor data acquisition system and the resolution of the spectrometer was about 0.8 eV. All the reflection spectra are obtained from the specular reflection spots satisfying surface resonance conditions.

Plasma parameters in atomic-emission spectral analysis of phosphate concentrates of the fission products

2019 ◽  
Vol 85 (2) ◽  
pp. 17-22
Author(s):  
M. I. Khamdeev ◽  
E. A. Erin
Keyword(s):  
Spectral Analysis ◽  
Chemical Composition ◽  
Reference Materials ◽  
Fission Products ◽  
Atomic Emission ◽  
Electric Arc ◽  
Physical Parameters ◽  
Arc Plasma ◽  
Atomic Emission Spectral Analysis ◽  
Excitation Processes

Physical parameters of electric arc plasma as well as their time dependences are calculated when analyzing phosphate precipitates of the fission products of irradiated nuclear fuel. Phosphate concentrates of the fission products are known for their complex chemical composition and high thermal and chemical stability. Hence, direct atomic emission spectral analysis of phosphate powders without transferring them into solutions is advisable. Different conditions of sample preparation and synthesis of the reference materials determine the different chemical forms of the elements to be determined. This, in turn, affects the kinetics of their evaporation in the electrode crate and excitation processes in the plasma. The known mechanisms of those processes cannot always be transferred to specific conditions of the given method of analysis thus entailing the necessity of studying the effect of the samples chemical composition on the results of determination, proper choice of spectroscopic carriers, detailed study of spectra excitation processes in spectral analysis, and analysis of the physical parameters of the electric arc plasma. We used the lines Zn I 307.206 nm and Zn I 307.589 nm to measure the effective temperature of the central hot sections of the arc in a range of4500 - 6500 K. NaCl, BaCl2 and NaCl + T1C1 were studied to reduce the effect of the sample elemental composition on excitation conditions of the spectra and their stabilization as a spectroscopic carrier. In control experiments we used carrier-free samples. The coincidence of the values of the plasma physical parameters within the measurement error not exceeding 20%, as well as the identity of the nature of the kinetic curves for samples of phosphate precipitates and synthetic reference materials prove their correctness. The result of the study substantiate correctness of the direct atomic-emission spectral procedure in analysis of phosphate concentrates of fission when using synthetic reference materials.

Theoretical modeling of excitation and de-excitation processes of Er in SiO2 with Si nanocrystals

2006 ◽  
Vol 121 (2) ◽  
pp. 222-225 ◽  
Author(s):  
A.A. Prokofiev ◽  
A.S. Moskalenko ◽  
I.N. Yassievich
Keyword(s):  
Theoretical Modeling ◽  
Si Nanocrystals ◽  
Excitation Processes

scholarly journals Properties of the Biexciton and the Electron-Hole-Plasma in Highly Excited GaN

1997 ◽  
Vol 2 ◽  
Author(s):  
J.-Chr. Holst ◽  
L. Eckey ◽  
A. Hoffmann ◽  
I. Broser ◽  
H. Amano ◽  
...  
Keyword(s):  
Chemical Vapor ◽  
Blue Laser ◽  
Basic Material ◽  
Organic Chemical ◽  
Electron Hole ◽  
Hole Plasma ◽  
Electron Hole Plasma ◽  
Wide Range ◽  
Gain Spectra ◽  
Excitation Processes

High-excitation processes like biexciton decay and recombination of an electron-hole-plasma are discussed as efficient mechanisms for lasing in blue laser diodes [1]. Therefore, the investigation of these processes is of fundamental importance to the understanding of the properties of GaN as a basic material for optoelectronical applications. We report on comprehensive photoluminescence and gain measurements of highly excited GaN epilayers grown by metal-organic chemical vapor deposition (MOCVD) over a wide range of excitation densities and temperatures. For low temperatures the decay of biexcitons and the electron-hole-plasma dominate the spontaneous-emission and gain spectra. A spectral analysis of the lineshape of these emissions is performed and the properties of the biexciton and the electron-hole-plasma in GaN will be disscused in comparison to other wide-gap materials. At increased temperatures up to 300 K exciton-exciton-scattering and band-to-band recombination are the most efficient processes in the gain spectra beside the electron-hole-plasma.

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