scholarly journals Effects of Magnetic and Electric Fields on Highly Excited Atoms

1984 ◽  
pp. 247-320 ◽  
Author(s):  
Charles W. Clark ◽  
K. T. Lu ◽  
Anthony F. Starace
Keyword(s):  
Electric Fields ◽  
Excited Atoms

The role of light quanta in the electric breakdown of gases

1954 ◽  
Vol 222 (1151) ◽  
pp. 490-508 ◽  
Keyword(s):  
Electric Fields ◽  
Wave Length ◽  
Short Wave ◽  
Gas Pressure ◽  
Atomic Data ◽  
Excited Atoms ◽  
Electron Multiplication ◽  
Alternating Electric Fields ◽  
Wide Range ◽  
Slow Electrons

The idea that multiplication of electrons by direct collisions with gas atoms can account for the starting of discharges has been found to be untenable in neon over a wide range of pressure and wave-lengths. Also, the dictum that wall processes can be neglected when the gas pressure is high appears to be a fallacy. The experiments leading to these conclusions were done with cylindrical glass vessels with plane ends and external electrodes and uniform alternating electric fields. With pressures from 2 to 200 mm Hg, as the wave-length was varied between 10 and 10 7 m, the starting field showed three plateaux, the lowest at short wave-lengths. Here for p > 50mm Hg the field per unit pressure was found to be constant and very low, namely, 0·6 V/cm mm Hg. Using even the most favourable energy distribution, the fraction of electrons exceeding ionization energy of about 21 eV is much too small to give electron multiplication by collision which can balance the losses by diffusion. However, there is a much larger fraction of electrons which can excite neon atoms to resonance or metastable levels. Thus a new picture emerges; a chance electron which is accelerated by the field excites neon atoms to about 16 eV. The emitted quanta which fall on the glass walls release photo-electrons which join the first electron, etc.; hence, not only are electrons multiplied but also quanta. When the concentration of excited atoms has become sufficiently great, the large number of slow electrons with energies > 5 eV can ionize the excited gas. Thus the starting field corresponds not to ionization by collision but to the onset of multiplication of quanta and photo-electrons during the first stage of the breakdown. The theory given leads to a relation between the starting field and its wave-length, the gas pressure, the size of the vessel, the nature of the gas and of the wall. Good numerical agreement with observations is found, the constants being taken from known atomic data. The concept of the electron multiplication sustained by quanta may have a bearing on other types of discharge in different gases.

Atom-based sensing of microwave electric fields using highly excited atoms: mechanisms affecting sensitivity

2019 ◽  
Author(s):  
James P. Shaffer ◽  
Harald Kubler ◽  
James Keaveney ◽  
Chang Lui ◽  
Jaime Ramirez-Serrano ◽  
...  
Keyword(s):  
Electric Fields ◽  
Excited Atoms

scholarly journals Coherently excited atoms in external electric fields

1975 ◽  
Vol 11 (3) ◽  
pp. 1114-1117 ◽  
Author(s):  
Maurice Lombardi ◽  
Marc Giroud ◽  
Joseph Macek
Keyword(s):  
Electric Fields ◽  
Excited Atoms ◽  
External Electric Fields

Photoinduzierte Stoßprozesse metastabiler Wasserstoffatome mit H2 im Energiebereich von 0,05 — 0,47 eV

1969 ◽  
Vol 24 (4) ◽  
pp. 587-596 ◽  
Author(s):  
F. J. Comes ◽  
U. Wenning
Keyword(s):  
Electric Fields ◽  
Cross Sections ◽  
Collision Cross Section ◽  
Translational Energy ◽  
Selective Absorption ◽  
Hydrogen Atoms ◽  
Excited Atoms ◽  
Hydrogen Molecules ◽  
Vibrational Levels ◽  
The Difference

Abstract Molecular hydrogen was excited by selective absorption of ultraviolet radiation of appropriate wavelength into the vibrational levels ν′ 3, 4, and 5 of the electronic D (1IIu)-state. For the radiation bandwidth chosen the molecule was only formed in the rotational levels J = 1 and 2 of the R-branch. The excited molecules decay by predissociation into two hydrogen atoms of translational energy which is equal to one half of the difference between the excitation and dissociation energies. One of the atoms is formed in its first excited state. The formation of the excited species can be proven by its fluorescence (Lymanα-radiation). As a result the measurements show, that the excited atoms are all in the metastable 2S-state and not in the short-lived 2P -state. Without electric fields these metastable atom s loose their excitation energy in collisions with the surrounding hydrogen molecules. One part (a) follows an induced transition to the electronic ground state by the emission of Lyα-radiation (1216 Å), the other part (b) is transformed to products or undergoes an energy transfer process without emitting Lyα-radiation. If a quenching field is applied spontaneous emission will compete with collisional deactivation, which allows the deactivation cross sections to be calculated. These cross sections are between 50 and 100 Å2 (a) and about 50 Å2 in case (b). In case (a) the collision cross section increases with the velocity of the particles whereas in case (b) a constant value was found.

Control of Metal Alloy Oxidation with Electric Fields

1973 ◽  
Vol 31 ◽  
pp. 164-165
Author(s):  
R. R. Dils ◽  
P. S. Follansbee
Keyword(s):  
Electric Fields ◽  
Oxidation Process ◽  
Base Alloy ◽  
Oxide Surface ◽  
Platinum Electrodes ◽  
Insulating Layer ◽  
Iron Base Alloy ◽  
Alloy Oxidation ◽  
Aluminum Oxide Layer ◽  
And Control

Electric fields have been applied across oxides growing on a high temperature alloy and control of the oxidation of the material has been demonstrated. At present, three-fold increases in the oxidation rate have been measured in accelerating fields and the oxidation process has been completely stopped in a retarding field.The experiments have been conducted with an iron-base alloy, Pe 25Cr 5A1 0.1Y, although, in principle, any alloy capable of forming an adherent aluminum oxide layer during oxidation can be used. A specimen is polished and oxidized to produce a thin, uniform insulating layer on one surface. Three platinum electrodes are sputtered on the oxide surface and the specimen is reoxidized.

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