H." Tawara

K. "Onda

K. Sakimoto

National Institute for Fusion Science (NIFS-Repository)

§20. Study of Elementary Collision Processes Related to Vibrationally Excited Molecules Onda, K. (Sci. Univ. of Tokyo) Sakimoto, K. (Insti. Space and Astron. Sci.) Tawara, H. In a presently pursued fusion reactor such as ITER, one of unresolved problems is how efficiently to exhaust thermal power and the He ash from the reactor region without degra-dation of the main plasma burning condi-tions. A plausible solution is sought in the ~nhancement of longitudinal plasma power and particle flows in the reactor chamber periphery located outside the main plasma torus. This intense directional scrape-off plasma flow concentrates large heat and par-ticle loads on the flux intercepting material surfaces in the divertor chamber. Reduc-tion of these loads can be achieved by us-ing atomic and molecular collision processes in the divert or region. Main components in the divertor chamber are H2 , H, He and their isotopic variance and their ions. It is highly probable that H2 molecules are in vi-brationally excited states. It is thus impor-tant to investigate collision processes related to vibrationally excited H2 molecules. Our method, 1 by which the Schrodinger equation describing collision processes be-tween an atom and diatomic molecule is nu-merically solved with quantum mechanically sufficient accuracy, aims specifically at inves-tigating chemical reaction and dissociation of the target molecule, and has been applied to a collinear collision of He and Ht (vi) and their isotopic combinations. The energy depen-dence of the dissociation and reaction prob-abilities has been studied at the total energy up to 10 eV, and interesting numerical results have been obtained. 2 In order to understand deeply these results in the physical point of view, we have further investigated the colli-sion process of He and Ht(vi) by dividing the interaction potential into two parts, that is, the one consisting of the sum of two body in-teraction potentials and the other consisting of the sum of many body interaction poten-tials except for two body ones. If we employ the full interaction potential, we have obtained the following results. Prob-abilities of vibrationally inelastic scatterings without any exception become smaller for all of the initial vibrational states at the total energy from the dissociation threshold to 10 eV. The probability of dissociation process for vi :::; 4 is very small, and the collision almost always ends up with a formation of HeH+, even if the total energy is increased up to 10 eV. If the initial vibrational state is above Vi = 1 f rv 13 depending on the total en-ergy, the dissociation of the Ht ion becomes the main process. On the other hand, if we take into account only two body part as the inteaction poten-tial, only vibrationally inelastic scatterings dominate over the dissociation of Ht (vi) for the initial vibrational state below vi= 4. The atom rearrangement process is almost com-pletely suppressed for Vi :::; 4, and competes with the dissociative one for Vi = 5 rv 10 at the total enegy up to 10 e V. These results show that the atom exchange reaction has been decisively caused by many body interactions in the collision of He and Ht (vi) for vi :::; 4, and give us an insight into physically understanding mechanism of chenaical reactions in collision between an atom and molecule. For vi ~ 5, two body in-teraction plays almost the same role as many body interaction in atom rearrangement and dissociation of the molecule. Dissociation of the molecule in 11 :::; vi can be caused mainly by two body interaction potential. A description of our method, further de-tails on these findings, and a full discussion of results shall be published soon. 2 References 1. K.Sakimoto and K.Onda, J.Chem.Phys. 100 (1994) 1171. 2. :K. Onda and K. Sakimoto, in preparation. 299 

Study of Elementary Collision Processes Related to Vibrationally Excited Molecules

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