Mechanism of the product vibrational-rotational state selectivity in a gas phase ion-molecule collision

J. Phys. B: At. Mol. Opt. Phys.

2001

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Geometrical and electronic structures of SF6 and SF6- have been determined using ab initio molecular orbital calculations in order to shed light on the mechanism of electron capture of SF6. The calculations (MP2/6-311G(d) + sp and MP2/6-311 + G(d) levels) showed that both SF6 and SF6- have Oh symmetry, while the S-F bond of SF6- is about 10% longer than that of SF6, indicating that the structure of SF6 is deformed along the S-F symmetric stretching mode by accepting an excess electron. The calculations showed that the adiabatic electron affinities of SF6 are positive (0.49-1.39 eV), which is in reasonable agreement with the experimental values (0.32-1.49 eV). The potential energy curve calculated as a function of an S-F bond of SF6- showed that SF6- is bound with respect to its dissociation limit (SF5- + F). The mechanism of electron capture of SF6 is discussed on the basis of the theoretical results.

Section: Introductionmentioning

confidence: 99%

Ab initioMO calculations of structures and electronic states of SF₆and SF₆^-

J. Phys. B: At. Mol. Opt. Phys.

2001

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“…Classical trajectory calculations, in general, are performed on an analytically fitted potential energy surface (PES). , However, it is not appropriate to predetermine the reaction surfaces of the present systems due to the large number of degrees of freedom (3 N − 6 = 102 for Bp and 3 N − 6 = 210 for the model compound of PVB, where N is number of atoms in the system). Therefore, in the present study, we applied direct ab initio trajectory calculation with all degrees of freedom to the ionization dynamics of Bp.…”

Section: Methodsmentioning

confidence: 99%

Dynamics of the Hole-Capture Processes in Biphenyl and Poly(4-vinylbiphenyl): A Direct ab Initio Trajectory Study

Kawabata

2003

J. Phys. Chem. B

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Direct ab initio trajectory calculations have been applied to the ionization (i.e., hole-capture) processes of biphenyl (Bp) in order to shed light on hole-capture processes of Bp and poly(4-vinylbiphenyl) (PVB). The static ab initio calculations at several levels of theory showed that the neutral Bp has a nonplanar structure with a twist angle between benzene rings in the range φ ) 38-50°. The potential energy curve for the twist rotation of benzene rings was shallow for Bp. This twist angle was changed to 18-21°in biphenyl cation (Bp + ), which has a more planar structure and a more tight potential shape than those of Bp. Full dimensional direct ab initio trajectory calculations showed that the structure of Bp is spontaneously changed after the ionization: the nonplanar structure was changed to planar one after 120 fs, and then the twist angle vibrated between -40°and +40°with a time period of about 500 fs. The C-C bond distance in the connection site between two benzene rings was immediately shortened after the hole capture of Bp, and it vibrated in the range 1.375-1.481 Å. Direct PM3 dynamics calculations for the model compound composed of two-monomer units of PVB indicated that a hole is localized on one of the biphenyl groups at time zero, and then it is delocalized over the two side-groups after the structural relaxation. The mechanism of hole capture in Bp and in PVB was discussed on the basis of theoretical results.

“…Usually, the classical trajectories have been made on an analytically fitted potential energy surface (PES) as previously carried out by several groups [13] and also by ourselves [14,15] (for a review article see [14]). However, it is not appropriate to predetermine the reaction surfaces of the present systems due to the large number of degrees of freedom (3N − 6 = 15 where N is the number of atoms in the system).…”

Section: Methodsmentioning

confidence: 99%

The ionization dynamics of SF₆: a full dimensional directab initiodynamics study

J. Phys. B: At. Mol. Opt. Phys.

2000

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The ionization dynamics of SF 6 , which plays an important role in plasma dry etching of semiconductors, has been investigated by means of full dimensional direct ab initio dynamics calculations. The SF + 6 ion, formed by the vertical ionization of SF 6 , decomposes directly into SF + 5 and F without complex formation. The dynamics calculations showed that 22% of the total available energy is partitioned into the relative translational mode between SF + 5 and F. The mechanism of the ionization of SF 6 and the etching of silicon by the F atom were discussed on the basis of the theoretical results.