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  • 1
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 7298-7305 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The structure of the HBr OCS van der Waals complex has been studied by Fourier transform microwave spectroscopy. The ground state complex is hydrogen bound and quasilinear with SCO–HBr atomic ordering. Spectra from five different isotopomers were observed and assigned. The wide amplitude bending angle of the hydrogen bromide was calculated from the nuclear quadrupole coupling constant χaa to be 25.2°. Second order quadrupole effects, centrifugal distortion in the nuclear quadrupole coupling constant Dχ, a spin–rotation interaction, CBr, and a spin–spin interaction, Daa, were all included in the Hamiltonian. The following spectroscopic constants have been determined for the H79Br OCS isotopomer: B¯=488.7948(4) MHz; DJ=2.167(6) kHz; HJ=1.19(3) Hz; χaa=387.14(1) MHz; Dx=6.79(14) kHz; CBr=0.55(13) kHz; and Daa=7.7(1.2) kHz. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 1022-1034 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: We describe a time-of-flight apparatus that uses core extraction to determine nascent product laboratory velocity distributions from which differential cross sections may be deduced. We emphasize the characterization of the instrument, the reaction conditions, and the calibration procedure. For this purpose, we have measured H-atom velocity distributions from HBr photolysis, as well as the H2(v′=4,J′=1) velocity distribution arising from the H+HBr reaction under quasi-monoenergetic collision conditions at 1.9 eV. Collisional energy spread and reagent internal state distributions were determined from the rotational and translational temperatures of the HBr photolytic precursor and the D2 diatomic reagent. The differential cross section for H+D2→HD(v′=2,J′=3)+D at 1.55±0.05 eV is presented and found to peak near 145°±10° with an approximate full width at half maximum (FWHM) of 40°. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2490-2498 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The photoloc technique with core extraction of the nascent product laboratory speed distribution in a Wiley–McLaren time-of-flight spectrometer has been used to measure differential cross sections for the reaction H+D2→HD (v′=2, J′=0,3,5)+D at collision energies ∼1.55 eV. We find that the peak of each angular distribution shifts from complete backward scattering toward side scattering as the rotational excitation of the product increases. We found the same trend in our previous study of H+D2→HD (v′=1, J′=1,5,8)+D at ∼1.70 eV. We conclude that the same type of correlation exists between impact parameter and rotational quantum number in both product vibrational manifolds. Further analysis of the HD (v′=2, J′) differential cross section data reveals, however, a clear tendency of this vibrational manifold to scatter sideways at lower J′ than HD(v′=1, J′). Within the framework of a line-of-centers model with nearly elastic specular scattering, this result implies that smaller impact parameters lead to more vibrationally excited products. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 1035-1042 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: A 1:4 mixture of HBr and D2 is expanded into a vacuum chamber, fast H atoms are generated by photolysis of HBr ca. 210 nm, and the resulting HD (v′, J′) products are detected by (2+1) resonance-enhanced multiphoton ionization (REMPI) in a Wiley–McLaren time-of-flight spectrometer. The photoloc technique allows a direct inversion of HD (v′, J′) core-extracted time-of-flight profiles into differential cross sections for the H+D2→HD(v′=1, J′=1,5,8)+D reactions at collision energies ca. 1.7 eV. The data reveal a systematic trend from narrow, completely backward scattering for HD (v′=1, J′=1) toward broader, side scattering for HD (v′=1, J′=8). A calculation based on the line of centers model with nearly elastic specular scattering accounts qualitatively for the observations. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 6634-6639 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: A 212.8 nm laser initiates the reaction H+D2→HD+D in a mixture of HBr and D2. A second laser state-selectively ionizes the HD(v′=3,j′) reaction product, allowing a determination of the speed distribution and the relative cross section in a velocity-sensitive time-of-flight mass spectrometer. From these measurements we construct differential and integral cross sections for H+D2→HD(v′=3,j′=0–7)+D at 1.64±0.05 eV collision energy. Although the integral cross sections do not show any unusual features, the differential cross sections reveal forward-scattered features that have not been observed in crossed-beam experiments. An analysis of the scattering features in HD(v′=3,j′=1–4) suggests that these states are dominated by classical hard-sphere scattering. This hard-sphere (direct recoil) mechanism, however, cannot account for the dominant forward scattering observed in HD(v′=3,j′=0). © 2002 American Institute of Physics.
    Materialart: Digitale Medien
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  • 6
    ISSN: 1476-4687
    Quelle: Nature Archives 1869 - 2009
    Thema: Biologie , Chemie und Pharmazie , Medizin , Allgemeine Naturwissenschaft , Physik
    Notizen: [Auszug] Extensive theoretical and experimental studies have shown the hydrogen exchange reaction H + H2 → H2 + H to occur predominantly through a ‘direct recoil’ mechanism: the H–H bonds break and form ...
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    Springer
    Origins of life and evolution of the biospheres 30 (2000), S. 513-517 
    ISSN: 1573-0875
    Schlagwort(e): asymmetric photolysis ; circularly polarized light ; elliptically polarized light ; synchrotran radiation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Geologie und Paläontologie
    Notizen: Abstract Previous investigations have shown the efficacyof right-(RCPL) and left-(LCPL) circularly polarized light inpromoting the asymmetric photolysis of racemic organic substratesand producing measurable enantiomeric excesses (e.e.s) whenphotolysis is incomplete. Synchrotron radiation, polychromaticand having out-of-plane components which are elliptically andultimately circularly polarized, has been suggested as auniversal source of RCPL and LCPL on a cosmic scale. The moreprevalent right-(REPL) and left-(LEPL) elliptically polarizedcomponents have never been investigated for similar capabilities.The present study, using a 212.8 nm laser beam to mimic thesynchtrotron radiation, explores the potential of REPL and LEPLin this context and finds a qualitative trend indicating thateach induces asymmetric photolysis in the same sense as RCPL andLCPL, but to a lesser degree.
    Materialart: Digitale Medien
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