H." Tawara

K. "Onda

K. Sakimoto

National Institute for Fusion Science (NIFS-Repository)

§3. Quantum Mechanical Study of Collinear Exchange Reaction and Dissociation Processes in Atom and Diatomic Molecule Collisions Onda, K. (Sci. Univ. of Tokyo) Sakimoto, K. (Insti. Space and Astron. Sci.) Tawara, H. It is now recognized that reliable collision data between H2 molecule and H, He, H2, or their ions are important to design efficient gas cooling divertors. It is highly probable that H2 molecules in divertor plasma are in vibrationally excited states. There is still very few studies on collision processes related to vibrationally ex-cited H2 molecules. In the previous study, the energy dependence of the dissociation process He + Hi ( v) ---+ He + H + H+ and of the reaction He + Hi ( v) ---+ HeH+(v') + H has been investigated over a wide range of the total energy from 2.2 to 10 eV. Our results have shown that collision dynam-ics strongly depends on the initial vibrational states of the molecule. Furthermore, the vibra-tional distribution of the product HeH+ ion is strongly correlated with the one of the initial H+· 2 lOll. In order to clarify whether these results are common in and characteristic of the He + Hi collision system or not, investigation into this collision system has been extended to collision systems of different isotopic variants, that is, 4He + H+ HD+ DH+ HT+ or TH+ under 2' ' ' ' the same collinear arrangement. These isotopic vbariants have the same electronic potential en-ergy surface. The reduced masses are, respec-tively, 0.822, 1.076, 1.076,1.231, and 1.231 in atomic mass units, and accordingly a relative collision velocity becomes slower in that order of the above mass combination at the same total energy. The number of vibrational eigenstates increases as the reduced mass of the molecular ion becomes larger. Skew angles in the mass scaled coordinate system are 39.3 for He + HT+, 43.1 for He + HD+, 50.8 for He + Hi, 61.9 for He + DH+, and 67.8 for He + TH+ in unit of 278 degrees. We are particularly interested in elucidating what parameter should control collision dynam-ics in different mass combinations. In the followings, we summarize very briefly the results obtained at this moment. In the He + HD+ collision system, probabilities of vibra-tionally inelastic scattering of HD+ with the ini-tial vibrational state v < 4 are always larger than those for exchange reaction and dissocia-tion processes in the range of the total energy Etot < 10 e V. Probabilites for dissociation of HD+ with v > 10 become larger than those for vibrationally inelastic scattering and exchange reaction in the range of the total energy Etot > 4 eV. In the He + DH+ collision system, probabili-ties for exchange reaction of DH+ with v > 3 are almost independent of Etot below 10 eV, and their values are about 0.15 - 0.25 depending on the initial vibrational states. Vibrationally inelastic scattering process dominates over ex-change reaction and dissociation processes at the total energy below 5 e V. In the He + HT+ collision system, probabili-ties for exchange reaction of HT+ are larger than those for vibrationally inelastic and dissociation process at the total energy Etot below the disso-ciation threshold. Probabilities for vibrationally inelastic scattering are always larger than those for exchange reaction and dissociation processe~ at the total energy Etot above the dissociation threshold. I In the He + TH+ collision system, probabili~ ties for vibrationally inelastic scattering of TH~ with v < 3 - 5 are larger than those for dissoci~ ation process Etot below 10 e V. : Although we have had new results for differen~ isotopic variants of He + Hi collision systems; it is difficult for us to understand systematically these results by taking account of the parame-ters stated above. A detailed description of our method, further details on these findings, and a full discussion shall be published[1]. References 1. K. Onda and K. Sakimoto, in preparation. 

Quantum Mechanical Study of Collinear Exchange Reaction and Dissociation Processes in Atom and Diatomic Molecule Collisions

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