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AbstractAbstract

[en] Theoretical studies have been carried out on two categories of molecular collision processes: (I) molecule scattering with a light incident particle-electron, and (II) molecule scattering with a heavy incident particle atom. For the electron-molecule scattering, a general approach, two-potential approach, has been formulated for elastic and vibrational transitions with intermediate- and high-energy impact electrons. In this approach, contributions to the scattering process come from the incoherent sum of two dominant potentials: a short-range shielded nuclear Coulomb potential from individual atomic center, and a permanent/induced long-ranged potential. Applications to e-N

_{2}, e-CO, and e-CO_{2}scatterings from 50-800 eV incident electron energy have yielded good agreement with absolutely calibrated experiments. This study has helped in understanding the physical effects responsible for the structure in the differential cross section as well as to gain a clear physical picture of the detail of the electron-molecule scattering process. The three-dimensional atom-molecule reactive collision has been studied quantum-mechanically within the T-matrix formalism with the adiabetic approximation. By formulating the problem in the body-fixed coordinate system, it was possible to study the scattering process with the rotationally pre-excited target molecule. Application to the D + H_{2}reaction on the ab initio Liu-Wiegbahn-Truhlar-Horowitz (LSTH) surface has been made. Scattering cross sections of the rotationally pre-excited target molecule are in general 2 to 3 times smaller than those of the ground state molecule. Various dynamical scattering attributes are averaged at the beam temperature of the experiment of Geddes, Krause and Fite (GKF) and have yielded good agreement with the GKF experimentPrimary Subject

Source

1980; 293 p; University Microfilms Order No. 80-20,622; Thesis (Ph. D.).

Record Type

Report

Literature Type

Thesis/Dissertation; Numerical Data

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AbstractAbstract

No abstract available

Primary Subject

Source

CEA, 75 - Paris (France); p. 495; ISBN 2-7272-0020-X; ; 1977; p. 495; North-Holland; Amsterdam, Netherlands; 10. international conference on the physics of electronic and atomic collisions; Paris, France; 21 - 27 Jul 1977; Published in summary form only.

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Book

Literature Type

Conference

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AbstractAbstract

No abstract available

Primary Subject

Source

CEA, 75 - Paris (France); v. 1 p. 495; ISBN 2-7272-0020-X; ; 1977; v. 1 p. 495; Commissariat a l'Energie Atomique; Paris, France; 10. International conference on the physics of electronic and atomic collisions (ICPEAC); Paris, France; 21 - 27 Jul 1977; Books of abstracts commercially available from North-Holland, Amsterdam, the Netherlands; Published in abstract form only.

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Book

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Conference

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AbstractAbstract

[en] The body fixed formulation of the adiabatic distorted wave theory is used to study the reactive collisions of the (D,H

_{2}) system. Cross sections are obtained on the ab initio potential surface from the threshold to 0.5 eV in relative translation energy for the case where the target molecule is in the first rotationally excited state. The present results of the ortho-hydrogen are qualitatively similar to but quantitatively different from the previous results of para-hydrogen. The statistically weighted cross sections and product state distributions are found in general agreement with the molecular beam experiment. The reaction rates are obtained by integration over the distribution function. From 150 to 750^{0}K where there are experimental data, the curvature in the Arrhenius plot of the calculated rate constants is in excellent agreement with experiment. However, the absolute magnitudes of the rate constants are smaller than the experimental onesPrimary Subject

Record Type

Journal Article

Journal

Journal of Chemical Physics; ISSN 0021-9606; ; v. 73(12); p. 6095-6107

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AbstractAbstract

[en] The adiabatic T matrix method is used to carry out a three dimensional quantum mechanical calculation for the reactive scattering of D+H

_{2}on an ab initio potential surface. Total and differential cross sections as well as final state distributions are obtained. When compared with adiabatic distorted wave results, agreement is good except the present total cross section is larger. When compared with trajectory calculations, agreement is also good except for the threshold behavior and the final state distribution. The rate constants obtained from the present total reaction cross sections are in very good agreement with measurements. With the analysis of the center of mass to laboratory transformation for the trajectory calculations and the comparison between those results and present ones, differential cross sections and final state distributions obtained in the present calculation are also seen to be in agreement with the molecular beam experimentPrimary Subject

Record Type

Journal Article

Journal

Journal of Chemical Physics; ISSN 0021-9606; ; v. 79(11); p. 5376-5385

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AbstractAbstract

[en] A formulation of atom-diatomic molecule (or molecular ion) collision on a single potential surface of ground electronic state of triatomic (or ionic) system containing identical nuclei is presented based on the formal multiarrangement channel collision theory. A properly symmetrized scattering matrix which is unitary over all arrangement channels is introduced. The matrix makes the formulation quite systematic. Furthermore, it enables us to extend the formulation efficiently to more general collision systems containing several species of the identical particles by partitioning the arrangement channels into collections of the indistinguishable ones. This is illustrated in the simple three particle atom--diatom system of the present work. Through the matrix, formulas of the optical theorem satisfied by the symmetrized cross sections are also obtained. The adiabatic electronic wave functions are found to be either symmetric or antisymmetric under interchange of nuclear coordinates. It is determined by the electronic states but is independent of the fermion or boson characteristic of the nuclear spin. Formulas of the properly symmetrized cross sections that arise from the nuclear spin statistics of the indistinguishable nuclei are obtained for the symmetric as well as the antisymmetric electronic wave function of the triatomic system. They are obtained in terms of either resultant nuclear spins of the molecules or individual nuclear spin quantum numbers

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Record Type

Journal Article

Journal

Journal of Chemical Physics; ISSN 0021-9606; ; v. 78(9); p. 5590-5605

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AbstractAbstract

[en] A general theoretical approach is proposed for the calculation of elastic, vibrational, and rotational transitions for electron-molecule scattering at intermediate and high-electron-impact energies. In this formulation, contributions to the scattering process come from the incoherent sum of two dominant potentials; a short-range shielded nuclear Coulomb potential from individual atomic centers, and a permanent induced long-range potential. Application to e-N

_{2}scattering from 50--500 eV incident electron energies has yielded good agreement with absolutely calibrated experiments. Comparisons with other theoretical approaches are made. The physical picture as well as the general features of electron-molecule scattering process are discussed within the framework of the two-potential approachPrimary Subject

Record Type

Journal Article

Journal

Physical Review. A; v. 19(1); p. 116-124

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AbstractAbstract

[en] A quantum mechanical approach is used to calculate the cross sections and rate constants of D+H

_{2}(v/sub α/=1,0) → DH(v/sub β/=0,1)+H. With v/sub α/=0, present results are in agreement with classical calculation. With v/sub α/=1, cross sections for the vibrational adiabatic transition (v/sub α/=1 to v/sub β/=1) is an order of magnitude larger than that for the vibrational nonadiabatic transition (v/sub α/=1 to v/sub β/=0). This result is in agreement with recent experiments but in disagreement with classical-trajectory calculationPrimary Subject

Record Type

Journal Article

Journal

Physical Review Letters; ISSN 0031-9007; ; v. 44(18); p. 1211-1214

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AbstractAbstract

[en] We present a formulation of the three-dimensional quantum mechanical reactive scattering of an atom and a rotationally excited diatomic target molecule within the framework of adiabatic distorted wave theory. This is an extension of previous work where only the rotationally ground initial state was treated while the final molecule could be in any state. The importance of the present formulation lies in the fact that the population of the rotationally excited target molecules is significant under ordinary experimental conditions. A method of obtaining exact and approximate adiabatic wave functions and energies is developed through the use of the body-fixed formulation of atom--diatomic molecule scattering. The integration in transition matrix with rotationally excited adiabatic wave function is again reduced to the three-dimensional integral by separating out the angular variables for the rigid motion of the plane for the atom--molecule system. Explicit integration formula is presented for the reactive transition matrix element. The computational feature of the present formulation is illustrated by evaluating the reactive cross section of the (D,H

_{2}) system. For 0→1 rotational transition, present calculations reproduced earlier results. For 1→1 rotational transition, for which no previous result of the adiabatic distorted wave theory is available, the present calculations yield qualitatively similar but quantitatively different angular dependence in the differential cross sections, as in those of the rotationally ground target molecule. Physical significances and further implication of the present formulation are discussedPrimary Subject

Record Type

Journal Article

Journal

Journal of Chemical Physics; ISSN 0021-9606; ; v. 73(9); p. 4381-4389

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AbstractAbstract

[en] We present an adiabatic transition matrix (T matrix) method of atom--molecule reactive scattering. In this method, the coupling between vibrational and rotational motions is taken into account for obtaining the adiabatic molecular wave functions. These wave functions are expanded in terms of the basis functions taken from the eigenfunctions of a double well potential. From the full potential surface in the linear configuration of three atoms, the double well potential is obtained. Convergence of the expansion is achieved for evaluating the adiabatic wave functions and two body atom--molecule interaction potential. Cross sections are computed with the T matrix method employing the converged adiabatic wave functions. Numerical results for the H+H

_{2}reactive cross section on an ab initio potential surface are presented. Results on D+H_{2}reaction will be reported in a subsequent paper. The differential cross sections and final state distributions computed from the present adiabatic T matrix method are similar to ones obtained from the adiabatic distorted wave approximation which we published earlier. However, the absolute cross section from the present approach is considerably larger than the previous one. The present results on the reactive cross section are in very good agreement with those obtained from a close coupling calculation. The present cross sections are much bigger than the classical ones in the threshold region. Among the cross sections from various T matrix approaches, the present one is the largest and seems to be most accuratePrimary Subject

Record Type

Journal Article

Journal

Journal of Chemical Physics; ISSN 0021-9606; ; v. 78(7); p. 4523-4532

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