Photodetachment of H– ion in a nonuniform electric field

2013 ◽  
Vol 91 (8) ◽  
pp. 650-657
Author(s):  
Yi-hao Wang ◽  
De-hua Wang ◽  
Jian-wei Li
Keyword(s):  
Electric Field ◽  
Cross Section ◽  
Closed Orbit ◽  
Analytical Formula ◽  
Negative Ions ◽  
Nonuniform Electric Field ◽  
Uniform Electric Field ◽  
Closed Orbits ◽  
Photodetachment Cross Section ◽  
The Cross

The photodetachment of H– ions in a nonuniform electric field has been investigated on the basis of closed orbit theory. Firstly, we give a clear physical description of the detached electron's movement in a nonuniform electric field. Then we put forward an analytical formula for calculating the photodetachment cross section of this system. Our study suggests besides the closed orbit previously reported for the photodetachment of H– in a uniform electric field, some additional closed orbits are produced owing to the effect of the nonuniform electric field. Compared with the photodetachment cross section of H– in a uniform electric field, the oscillation in the cross section of our system becomes much more complicated and the cross section exhibits a multiperiodic oscillatory structure. To show the relation between the oscillation in the photodetachment cross section and the detached electron's classical closed orbits clearly, we make a Fourier transformation for the scaled photodetachment cross section of this system. Each peak in the Fourier transformed cross section corresponds to the contribution of one closed orbit. This study provides a new understanding of the photodetachment of negative ions in the presence of a nonuniform electric field.

Photodetachment of the H– ion in a forced harmonic potential

2020 ◽  
Vol 98 (9) ◽  
pp. 883-892
Author(s):  
De-hua Wang
Keyword(s):  
Electric Field ◽  
Cross Section ◽  
Closed Orbit ◽  
Negative Ions ◽  
Resonance Phenomenon ◽  
Harmonic Potential ◽  
Outgoing Wave ◽  
Harmonic Frequency ◽  
Classical Motion ◽  
Photodetachment Cross Section

The photodetachment of a H– ion in a forced harmonic potential driven by a general time-dependent oscillating electric field has been investigated in the semi-classical closed orbit theory for the first time. It is found that the driven electric field frequency can affect the photodetachment cross-section of this system greatly. If the frequency of the driving electric field is equal to the harmonic frequency, a resonance phenomenon occurs in the classical motion of the detached electron. The interference effect between the returning electron wave travelling along the closed orbit with the initial outgoing wave gets stronger, causing the photodetachment cross-section to oscillate in a complicated manner. When the frequency of the driving electric field is unequal to the harmonic frequency, the driving electric field can weaken or strengthen the oscillatory structure in the photodetachment cross-section. In addition, the strength and initial phase in the driving electric field can also influence the photodetachment dynamics of the system. Our work provides a new method for controlling the photodetachment of negative ions in a harmonic potential and may guide future experimental research for cavity dynamics or in the ion trap.

Photodetachment of H– ion in perpendicular electric and magnetic fields near a metal surface

2014 ◽  
Vol 92 (10) ◽  
pp. 1241-1248 ◽  
Author(s):  
De-hua Wang
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Electric Field ◽  
Metal Surface ◽  
Cross Section ◽  
Closed Orbits ◽  
Electric And Magnetic Fields ◽  
Oscillatory Structure ◽  
Photodetachment Cross Section ◽  
The Magnetic Field

The photodetachment of the H– ion in perpendicular electric and magnetic fields near a metal surface has been investigated on the basis of the semiclassical closed-orbit theory. Firstly, we give a clear physical picture of the detached electron’s movement and find out the closed orbits of this system. Then we put forward an analytical formula for calculating the photodetachment cross section. It is found that the perpendicular electric and magnetic fields can produce some interesting effects. As the magnetic field is relatively weak, the influence of the electric field and the electrostatic potential dominates and the oscillatory structure in the photodetachment cross section exhibits a smoothly oscillating curve. As we keep the electric field and the ion–surface distance unchanged, with the increase of the magnetic field strength, the number of closed orbits is increased and the oscillatory structure in the photodetachment cross section is characterized by broad Landau level envelops. Therefore, we can use the perpendicular electric and magnetic fields to control the photodetachment of H– near a metal surface. Our study may guide future experimental research on the photodetachment microscopy of negative ion in external fields near surfaces.

The Design and Simulation for a Novel Electroosmotic Micromixer

2006 ◽  
Author(s):  
Hongjun Song ◽  
Xie-Zhen Yin ◽  
Dawn J. Bennett
Keyword(s):  
Electric Field ◽  
Cross Section ◽  
Chemical Reactions ◽  
Electroosmotic Flow ◽  
Chaotic Advection ◽  
Microfluidic Systems ◽  
Mixing Effect ◽  
Passive Mixers ◽  
The Cross ◽  
External Forces

The analysis of fluid mixing in microfluidic systems is useful for many biological and chemical applications at the micro scale such as the separation of biological cells, chemical reactions, and drug delivery. The mixing of fluids is a very important factor in chemical reactions and often determines the reaction velocity. However, the mixing of fluids in microfluidics tends to be very slow, and thus the need to improve the mixing effect is a critical challenge for the development of the microfluidic systems. Micromixers can be classified into two types, active micromixers and passive micromixers. Passive micromixers depend on changing the structure and shape of microchannels in order to generate chaotic advection and to increase the mixing area. Thus, the mixing effect is enhanced without any help from external forces. Although passive micromixers have the advantage of being easily fabricated and requiring no external energy, there are also some disadvantages. For example, passive mixers often lack flexibility and power. Passive mixers rely on the geometrical properties of the channel shapes to induce complicated fluid particle trajectories thereby enhancing the mixing effect. On the other hand, active micromixers induce a time-dependent perturbation in the fluid flow. Active micromixers mainly use external forces for mixing including ultrasonic vibration, dielectrophoresis, magnetic force, electrohydrodynamic, and electroosmosis force. However, the complexity of their fabrication limits the application of active micromixers. In this paper we present a novel electroosmotic micromixer using the electroosmotic flow in the cross section to enhance the mixing effect. A DC electric field is applied to a pair of electrodes which are placed at the bottom of the channel. A transverse flow is generated in the cross section due to electroosmotic flow. Numerical simulations are investigated using a commercial software Fluent® which demonstrates how the device enhances the mixing effect. The mixing effect is increased when the magnitude of the electric field increased. The influences of Pe´clet number are also discussed. Finally, a simple fabrication using polymeric materials such as SU-8 and PDMS is presented.

Study of Electric Field-Induced Evaporation Like Process and Nucleation in Nanoscale

2019 ◽  
Vol 141 (6) ◽  
Author(s):  
M. B. Darshan ◽  
Pratyush Agarwal ◽  
Dhiraj Indana ◽  
Saikat Datta ◽  
Ravi Kumar ◽  
...  
Keyword(s):  
Electric Field ◽  
Water Surface ◽  
Temporal Evolution ◽  
Temperature Fluctuations ◽  
High Heat ◽  
Density Variation ◽  
Nonuniform Electric Field ◽  
Uniform Electric Field ◽  
Water Molecules ◽  
Dynamics Simulations

A proposal is made to demonstrate features of thermodynamic evaporation at the nanoscale using only an external electric field. The consequences of exposure to both uniform and nonuniform electric field on the water nanofilms are analyzed through molecular dynamics simulations. The temporal evolution of temperature and molecular nucleation under uniform electric field resembles evaporation at high heat. The temperature fluctuations of the system are analyzed from the density variation of the system, which has received no heat input from outside. Evaporation like process and nucleation from the water surface is described as a systematic polarization of the water molecules in the presence of electric field. The nucleation of the vapor bubble with a nonuniform electric field also shows similarity with heat-induced pool boiling. The reason behind isolated nucleation is analyzed from the temperature map of the system at different time instants. Possible surface instabilities due to the exposure of electric field on water nanolayer are also elaborated for both uniform and nonuniform cases.

Photodetached electron spectrum of H- near a surface having spherical dent

2015 ◽  
Vol 14 (08) ◽  
pp. 1550063 ◽  
Author(s):  
Muhammad Haneef ◽  
Bakhtawar ◽  
Suneela Arif ◽  
Jehan Akbar ◽  
Nasrullah Shah
Keyword(s):  
Cross Section ◽  
Electron Flux ◽  
Focal Length ◽  
Negative Ions ◽  
Negative Ion ◽  
Concave Surface ◽  
Radius Of Curvature ◽  
Imaging Method ◽  
Surface Distance ◽  
Photodetachment Cross Section

The detached electron flux and photodetachment cross section are derived using the theoretical imaging method and quantum approach for system comprising of hydrogen negative ion ([Formula: see text]) placed near a surface having spherical dent. The dent is modeled like a spherical concave surface. It is observed that the spherical dent generates additional oscillatory and smooth structure in the detached electron flux and photodetachment cross section, respectively. The radius of curvature, inter-ion surface distance and the dent factor strongly manipulate the results. When the inter-ion surface distance is equal to the focal length of the concave surface, the detached electron flux and photodetachment cross section are not well behaved. The photodetachment cross section is also not well behaved for the inter-ion surface distance equal to the radius of curvature. The focus and center of curvature of the concave surface act as a spherical singularity. This study gives new understanding on the photodetachment of negative ions in the vicinity of concave surfaces.

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