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chemical terms

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synonym Recombine (recombination) generally refers to recombination

Recombination, a chemical term, also known as recombination, is used in both physics and chemistry.

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Foreign name: recombination

Alias: Recombine
Category: chemical terms

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（1） From two growth Free radical Combine to form one Saturated macromolecule The termination of the reaction is called recombination.

（2） Electrons in semiconductors receive light Acting from Price band Fired to conduction band , created the electronic- hole Yes, the solid surface may pass through“ Composite center ”Capture a minority carrier and Majority carrier , causing Electron hole pair This process is called recombination.

(III) welding arc The positive and negative charged particles (positive ions, negative ions, electrons) in space meet and combine under certain conditions Neutral particle The process of is called recombination.

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Positive ions in gas are the same as free electron Or negative ion collision Neutral atom Or molecular processes. The former is called electron ion recombination, or electron recombination for short; The latter is called ion ion recombination, or ion recombination for short.

Composite is ionization It is an important process to reduce the number of charged particles in the gas. The number of charged particles per unit time and per unit volume that disappear due to recombination and the density of positive, negative ions or electrons after ionization in gas stops n +, n - is proportional,

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usually n +=N -=n, so

Composite coefficient

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Scale factor

α Is called composite coefficient, dimension L3T-1, which is a macro parameter characterizing the recombination process. usually

The electron recombination coefficient and ion recombination coefficient are represented by α e and α i respectively. The recombination probability is closely dependent on the relative velocity of positive and negative charged particles. Anionic relative velocity Small, they have enough time to approach, and the chance of recombination is usually much greater than that of electrons and ions, so α i is much greater than α e, Order of magnitude 10-6, 10-8~10-10 respectively.

Electron ion recombination

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Release of composite energy, if photon This recombination process is called Radiation recombination ； If transferred to a third party (other atom , molecule or electron), it is called three body recombination. When there is a third party, three body recombination is more likely than radiation recombination. Therefore, at low pressure The discharge tube In the case of high pressure, recombination usually occurs more on the pipe wall, and more occurs inside the gas volume. In addition, when molecules and ions recombine with electrons, recombination energy may also make molecules dissociation , called dissociative recombination.

Ion ion recombination

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Interionic relative velocity It is closely related to air pressure. stay Low atmospheric pressure Lower, Ion Mean free path It is very long and has high relative speed. Even if it meets, it may not be able to recombine. However, British physicists J. J. Thomson It is proposed that if the neutral point is the same as the nearby neutral point Molecular collision , their relative velocity will become slower and close to the thermal velocity, and the ionic electric field will allow them to have enough time to close, and recombination can occur. Derived from this, α I is inversely proportional to the average free path of ions, and therefore increases with the increase of air pressure. stay High barometric pressure The positive and negative ions can only meet after multiple collisions, the relative velocity is lower than the thermal velocity, and its value is determined by the mobility Decision, so α I is proportional to the mobility, so it decreases with the increase of air pressure. This is a French physicist P. Langevin Results obtained. Both theories have been proved by experiments, α The maximum value of i occurs at about 1 atmosphere. The energy released when two slow ions recombine is almost equal to the total energy absorbed when forming positive and negative ions, that is, equal to ionization energy Subtract the electron affinity potential of negative ions, which may be transferred to photon （ Radiation recombination ）, or transferred to a third party (three body recombination), which may also become Neutral atom Excitation energy or kinetic energy However, it is unlikely to become kinetic energy.

Research process

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Study the composite process for understanding the ionosphere Understand the formation and nature of the sun Corona , the sun's outer atmosphere, and High temperature plasma The act of waiting is of great significance.

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