Charge exchange recombination

The process of charge exchange occurs by capture of a bound electron from neutral hydrogen by H-like ions followed by radiative decay. As in the case of radiative recombination or cascades in He-like ions, the contribution of charge transfer is stronger to the triplet lines than to the resonance line w. The emission via charge-transfer is determined by  

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To determine the relative abundance of ionization stages, there are no alternatives to spectroscopic measurements. In fusion devices, the distribution of the ionization stages deviates from coronal equilibrium, due to transport and finite confinement of the ions as well as charge exchange recombination with neutral hydrogen. Both the particle transport and the diffusion reduce the... 

Fig. 8.5. Comparison between the central ion temperature measured by the X-ray spectrometer and the ion temperature by charge exchange recombination spectroscopy (CXRS) [3]...

The authors are glad to thank many scientists, who have contributed to the results. The TEXTOR team, where the measurements were performed and highly reproducible plasmas were provided, especially to Dr. W. Biel, who did the experiments on the transport properties of TEXTOR, Prof. L. Vainshtein, Dr. A. Urnov and F. Goryaev provided us with the results of atomic data calculation. Dr. N. Badnell trained one of us (O. M.) to get the results on dielectronic recombination using atomic codes. Dr. S. Fritzsche put our attention to the cascades within the Li-like ions and Prof. R. Janev discussed the charge exchange recombination processes. Princeton Plasma Physics Laboratory supported the measurements on TEXTOR, both by cooperation with Dr. M. Bitter, and loan of X-ray detectors. 

If the recombination leaves the atom in a high atomic state, the recombination energy will be so low that charge exchange cannot take place. Such recombination energies are not included in Table II. 

If no transfer of translational energy occurs, then the charge exchange process probably takes place when the distance between the ion and the molecule is large. This means, however, that the ion and the molecule can be considered as isolated from each other, and therefore, the recombination process of the ion and the ionization process of the molecule must obey the spectroscopic transition laws. On the other hand, if a large transfer of translational energy takes place, then the process probably takes place when the distance is small, and possibly then all selection rules break down. 

Most of the electron and ion impact reactions that are included in this code are listed in Table II. Added to this are the elastic collisions SiHa -1- e [274] and H2 -f e [275], the recombination SiHJ + SiH 2SiH3 [214], and the charge exchange HJ -f H2 -1- H [193]. Note that disilane is not included. The... 

At the anode, the charge exchange will also occur. Some electrons will recombine with the trapped positive ion, but most electrons may be trapped on the surface. The energetic electron may form the activated site on the surface ... 

Specific features of corrosion processes at semiconductors (as against to metals) are caused by the fact that charge carriers of both signs, namely conduction band electrons and valence band holes, take part in charge exchange between a solid and a solution. Therefore, the condition of Eq. (43) is insufficient, so account should be made of charge balance for each type of the carriers because equilibrium between the bands, which is established via generation-recombination processes, may not be reached. 

The k and j satellites are the strongest dielectronic satellites to the He-like lines, the q, r, s and t satellites have strong contributions due to inner-shell excitation from the Li-like ground state. Besides the dominant collisional excitation of He-like ions in the ground state, recombination processes (radiative, dielectronic and charge exchange) of H- and He-like ions, inner-shell excitation of the Li-like ions and, in the case of the z line, also inner-shell ionization process contribute to the intensity of the He-like lines. We will discuss these processes in detail. 

Fig. 1. Interstellar formation scheme illustrating the CH, CH, C H and higher hydrocarbon cycle. The left side of the reaction cycle pertains to tenous clouds (Uj, 100 cm ), whereas the right hand side is more appropriate to areas where is present, i.e. dense molecular clouds (n 10 -10 cm" ). The thick arrows indicate assumed preferential reaction paths leading to the higher order hydrocarbons. The following processes are involved (v, e) photoionization (v, H) photodissociation (e, v) radiative recombination (H) (Hj, v) radiative association (e, H), (e, Hj) dissociative electron recombination. (Hj, H) hydrogen abstraction reaction (C, H) charge exchange (M, M ) metal charge exchange metal = Mg, Fe, Ca, Na,...

Neutralisation of CH can be achieved, — as in the case NH — by charge exchange reaction with low ionization metals, such as Fe, Ca, Mg, Na,... In dense clouds there is also the possibility of radiative association followed by dissociative electron recombination to reach neutral CH4. 

Pyrolysis reactions are undoubtedly occurring after combustion, and chemi-ionization may be occurring in addition to charge exchange reactions between primary ions, such as CsHs, and light hydrocarbons. Hence, the chemi-ion profile would not decay necessarily as it does in leaner combustion, where recombination begins to dominate ion formation. Instead, a different sequence of chemi-ion reactions may become important, with the precursor being C2, rather than CH. 

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