Role of Molecular Hydrogen in Recombination MAR

The chain of reactions which plays a key role in MAR is the vibrational excitation of molecules by electron impact, then an ion conversion H2(w) + H+ — + H, followed by dissociative recombination + e —  

H + H [25]. The excited atom decays by spontaneous emission or electron collisions into the ground state. Other possibilities are re-ionization of the excited atom or both atoms are ionized, these processes are the Molecular Assisted Dissociation (MAD) and Molecular Assisted Ionization (MAI), respectively. At the end of the MAR chain, one electron-ion pair is recombined 

On the basis of these investigations, it is concluded that the overall contribution of molecules to recombination is in the order of some percent. However, it has to be kept in mind that the vibrational population plays a key 

While these investigations succeeded in a better qualitative understanding of the role of molecules in a divertor, it has to be kept in mind that quantitative predictions may be different for hydrogen and deuterium. Concerning deuterium, the vibrational levels and some selected rate coefficients have to be replaced in the codes and in addition the application of isotopic relations has to be critically reviewed. Another aspect is the influence of surfaces (particularly carbon material) on the vibrational population of the molecule (see Sect. 4.4.2). 

The vibrational population of hydrogen molecules in the ground state opens a manifold of low energy channels so that the knowledge of this parameter 

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