H." Tawara

K. "Onda

National Institute for Fusion Science (NIFS-Repository)

§7. Theoretical Study of Elementary Collision Processes Related to Vibrationally Excited Molecules: A Case Study of a Collinear Collision of H with H 2 ( v) Onda, K. (Sci. Univ. of Tokyo) Tawara, H. One of unresolved problems in a presently pursued fusion reactor such as ITER is how we can efficiently exhaust thermal power and the He ash from the reactor region without degradation of the main plasma burning con-ditions. The enhancement of longitudinal plasma power and particle flows is considered to be a plausible solution of this problem in the reactor chamber periphery located out-side the main plasma torus. This intense di-rectional scrape-off plasma flow concentrates large heat and particle loads on the flux in-tercepting material surfaces in the divertor chamber. Reduction of these loads can be achieved by using atomic and molecular col-lision processes in the divertor region. Main components in the divertor chamber are H2, H He their isotopic variance, and their ions. ' ' It is highly probable that H2 molecules are in vibrationally excited states. It is thus impor-tant to investigate collision processes related to vibrationally excited H2 molecules. We numerically solve the Schrodinger equation1 describing collision processes be-tween an atom and diatomic molecule with quantum mechanically sufficient accuracy. We have applied our method to a collinear collision of H with H2( vi) and their isotopic combinations, and specifically aim at inves-tigating chemical reaction and dissociation of the target molecule in this collision sys-tem. The energy dependence of the dissoci-ation and atom exchange reaction probabili-ties has been studied at the total energy up to 10 e V, 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 H and H2( vi) by dividing the 264 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. Non-reactive vibrational transition process dom-inates over the atom exchange reaction and dissociation processes for the initial vibra-tional states below vi ~ 4 at the total energy up to 10 e V. The probability of the dissoci-ation process for vi ~ 4 is very small, even if the total energy is increased up to 10 e V, which is higher than about 2 times of the dis-sociation energy. The reaction probability is also small for all the initial vibrational states of H2 at the total energy above the dissoci-ation threshold. This small reaction pro ba-bility for the collision of H with H2( vi) con-trasts with the large one3 for the collision of He with Hi(vi)· This should be understood by taking account of the difference in the non-additive many body interaction potentials be-tween these two collision systems.4 If the ini-tial vibrational state is above Vi = 11 rv 13 de-pending on the total energy, the dissociation of H2 becomes the main process. The prob-ability of the non-reactive vibrational transi-tion process is larger than that of the atom exchange reaction for these initial vibrational states. A description of our method, further de-tails on these findings, and a full discussion of results shall be published soon. 2 Difference in collision dynamics between He + Hi (vi) and H + H2( vi) will be further discussed and reported in detail. 4 References 1. K.Sakimoto and K.Onda, J.Chem.Phys. 100 (1994) 1171. 2. K. Onda, in preparation. 3. K. Onda and K. Sakimoto, submitted for publication. 4. K. Onda and K. Sakimoto, in preparation. 

Theoretical Study of Elementary Collision Processes Related to Vibrationally Excited Molecules: A Case Study of a Collinear Collision of H with H2 (ホス)

Theoretical Study of Elementary Collision Processes Related to Vibrationally Excited Molecules: A Case Study of a Collinear Collision of H with H2 (ホス)

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