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Digitale Medien

Cluster approach to structure of surfaces and chemisorption (1988)

Ellis, D. E. ; Guo, J. ; Cheng, H. P.

s.l. : American Chemical Society

The @journal of physical chemistry 〈Washington, DC〉 92 (1988), S. 3024-3028

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Quelle: ACS Legacy Archives

Thema: Chemie und Pharmazie , Physik

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1021/j100322a002

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2

Digitale Medien

A photoion–photoelectron coincidence study of Arn (n=2–4) (1989)

Norwood, K. ; Guo, J.-H. ; Ng, C. Y.

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 90 (1989), S. 2995-3003

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: Photoion–photoelectron coincidence (PIPECO) spectra for Ar+n (n=2–4) in the wavelength region of 750–875 A(ring) have been measured at different nozzle stagnation pressures. The ionization energies (IE) for the ground Ar+2[I(1/2)u] and Ar+3[I(1/2)u] states are determined to be 14.518±0.017 eV (854±1 A(ring)) and 14.350±0.033 eV (864±2 A(ring)), in agreement with the findings of previous photoionization experiments. The IE for Ar+2[II(1/2)u] is found to be (approximately-less-than)15.83 eV (783 A(ring)). The observation of the Ar+2[II(1/2)u] PIPECO band supports the interpretation that Ar+2[II(1/2)u] is metastable with a lifetime longer than 47 μs, a value in accord with the calculated radiative lifetime of 90.9 μs for the II(1/2)u →I(1/2)g transition. The PIPECO spectrum for Ar+2 is dominated by autoionization structure similar to that resolved in the photoionization efficiency spectrum for Ar+2, indicating that a significant fraction of electrons produced by these autoionizing states are slow electrons with near-zero kinetic energies. Evidence is found that metastable Ar+3 and Ar+4 ions formed by photoionization of Ar3 and Ar4 at energies above the Ar+2[I(1/2)u]+Ar(1S0) and Ar+3[I(1/2)u]+Ar(1S0) dissociation limits may live longer than 58 and 66 μs, respectively. We suggest that the formation of Ar+3 in metastable electronic states may be responsible for the long dissociation lifetimes of Ar+3 observed in this experiment.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.455901

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3

Digitale Medien

A photoion–photoelectron coincidence study of (CO)2 and (CO)3 (1989)

Norwood, K. ; Guo, J.-H. ; Luo, G. ; [weitere]

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 90 (1989), S. 6026-6033

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: The photoion–photoelectron coincidence (PIPECO) spectra for (CO)+2 in the wavelength region of 620–990 A(ring) have been obtained at different nozzle stagnation pressures (P0). The ionization energy for (CO)2 to CO+(X˜)⋅CO is determined to be (approximately-less-than)12.73±0.05 eV (974±4 A(ring)), indicating that CO+(X˜)⋅CO is bound by more than 1.29 eV. The PIPECO measurements also provide evidence that CO+(A˜,B˜)⋅CO are bound with dissociation energies 〉0.3 eV. At P0≤200 Torr and a nozzle temperature (T) of 120 K, nozzle expansion conditions which minimize the formation of (CO)n (n≥3), the intensities for the CO+(A˜,B˜)⋅CO PIPECO bands are found to be negligibly small compared to that for the CO+(X˜)⋅CO PIPECO band. This observation supports the conclusion that the excited CO+(A˜,B˜)⋅CO ions are dissociative, with dissociation lifetimes〈42 μs. This conclusion is contrary to that of the preliminary study which is based on the PIPECO spectrum for (CO)+2 measured at P0=350 Torr and T=120 K. Assuming that the radiative lifetimes of CO+(A˜ or B˜) and CO+(A˜ or B˜)⋅CO are identical, we estimate that the dissociation lifetimes for CO+(A˜)⋅CO and CO+(B˜)⋅CO are (approximately-less-than)4 μs and (approximately-less-than)50 ns, respectively.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.456368

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Digitale Medien

A photoion–photoelectron coincidence study of (CO)2 (1988)

Norwood, K. ; Guo, J.-H. ; Luo, G. ; [weitere]

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 88 (1988), S. 4098-4099

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: The photoion–photoelectron coincidence (PIPECO) spectrum for (CO)+2 has been measured in the wavelength region of ∼600–1 000 A(ring). The lower limits for the bond dissociation energies of CO+ (X˜)⋅CO, CO+ (A˜)⋅CO, and CO+ (B˜)⋅CO are determined to be 29.8, 17, and 16 kcal/mol, respectively. Evidence supporting the existence of long-lived (CO)+2 states with dissociation lifetimes 〉40 μs at energies above the CO+ (X˜,v=0)+CO asymptote is found. The dissociative lifetimes of CO+ (A˜)⋅CO and CO+(B˜)⋅CO are estimated to be longer than 4 μs and 50 ns, respectively.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.453814

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5

Digitale Medien

Electronic structures of the π-π type charge-transfer complexes of pyridine with boron trihalides (1985)

Ji-Min(J. M. Yan), Yan ; Jian-Guo (J. G. Zhao), Zhao

New York, NY : Wiley-Blackwell

International Journal of Quantum Chemistry 27 (1985), S. 465-473

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ISSN: 0020-7608

Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie

Notizen: The electronic structures of the π-π type complexes of pyridine with boron trihalides have been studied by means of IEHMO calculation. The results indicate that BX3(X = F, Cl, Br, I) tends to react with C5H5N in a planar configurations against the plane of C5H5N. The most stable configurations of complexes are at 60° of orientation angle ϕ for X = Cl, Br, I, but at 0° for X = F. A linear relationship between In Eb, the logarithm of rotation potential barriers, and the radii of halogen atoms r0 has been observed, and has been deduced from Morse potential function. In the complex, the donating properties of BX3 have an increase from X = F to I, and BF3 functions as an acceptor, but the others as donors. It has been shown that every energy level of the complex is corresponding to that of the donor or the acceptor, which we have discussed by the perturbation theory. The bonds between D and A appear essentially as π-π type but not pure.

Zusätzliches Material: 3 Ill.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/qua.560270411

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6

Digitale Medien

Microemulsion polymerization of styrene (1989)

Guo, J. S. ; El-Aasser, M. S. ; Vanderhoff, J. W.

Bognor Regis [u.a.] : Wiley-Blackwell

Journal of Polymer Science Part A: Polymer Chemistry 27 (1989), S. 691-710

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ISSN: 0887-624X

Schlagwort(e): Chemistry ; Polymer and Materials Science

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie

Notizen: Initiation of polymerization in styrene oil-in-water microemulsions by water-soluble potassium persulfate of oil-soluble 2,2′-azobis-(2-methyl butyronitrile) at 70°C gave stable latexes which were bluish and less translucent than the original microemulsions. The effects of initiator concentration, polymerization temperature, and monomer concentration on the kinetics, particle size distributions, and molecular weight distributions were investigated. The kinetics of polymerization were measured by dilatometry. In all cases, the polymerization rate shows only two intervals, which increased to a maximum and then decreased. There was no apparent constant rate period and no gel effect. A longer nucleation period was found for polymerizations initiated by potassium persulfate as compared to 2,2′-azobis-(2-methyl butyronitrile). The small latex particle size (20-30 nm) and high polymer molecular weight (1-2 × 106) implies that each latex particle consists of two or three polystyrene molecules. The maximum polymerization rate and number of particles varied with the 0.47 and 0.40 powers of potassium persulfate concentration, and the 0.39 and 0.38 powers of 2,2′-azobis-(2-methyl butyronitrile) concentration, respectively. This is consistent with the 0.4 power predicted by Smith-Ewart Case 2 kinetics. Microemulsion polymerizations of styrene-toluene mixtures at the same oil-water phase ratio gave lower polymerization rates and lower molecular weights, but the same latex particle size as with styrene alone. A mechanism is proposed, which comprised initiation and polymerization in the microemulsion droplets, by comparing the kinetics of microemulsion polymerization with conventional emulsion and miniemulsion polymerization systems.

Zusätzliches Material: 12 Ill.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/pola.1989.080270228

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