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  • American Institute of Physics (AIP)  (2)
  • 1995-1999  (2)
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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 598-605 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Photolysis of HCl adsorbed on LiF(001) was studied by means of hydrogen Rydberg-atom time-of-flight (HRTOF) spectroscopy. Experiments were performed using 193.3 nm excimer laser radiation or 121.6 nm tripled dye-laser radiation for photolysis. The H-atom translational energy distributions using 193.3 nm (6.41 eV) radiation showed three main features: a high-energy channel corresponding to elastically scattered H atoms (EL) peaked at 1.85 and 1.65 eV (leaving behind Cl and Cl*, respectively); a second channel ∼1.2 eV lower in energy resulting from surface-aligned inelastic collisions (INEL, peaking at 0.6 eV); and a thermalized channel thought to be the product of multiple collisions and trapping of the scattered H. For 121.6 nm (10.2 eV) photolysis, the H-atom translational energy distributions showed four features: EL, with a maximum at 5.5 eV (the Cl and Cl* channels could not be separated at this high recoil energy); INEL(1), peaking at 3.2 eV; a more complex inelastic pathway, INEL(2), with a maximum at 0.5 eV; and, finally, a thermalized channel. Angular distributions for the elastically scattered H atoms indicated that they scattered from F− in the underlying LiF(001) at 40 and 48° off-normal for photodissociation of HCl(ad) at 193.3 and 121.6 nm, respectively. These two angles are far from 71°, the angle that would be observed from specular scattering of the H atom from the surface plane; this is strong evidence for the localized atomic scattering (LAS) identified in earlier studies performed in this laboratory. It appears that the higher the energy of the H projectile, the deeper it penetrates into the impacted surface atom, giving rise to the larger scattering angle. As in previous work, an exchange reaction was invoked to explain the ∼1.2 eV energy loss in the INEL(1) channel, together with observed retention of direction in H following this strongly inelastic encounter. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 3129-3134 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Hydrogen Rydberg-atom time-of-flight spectroscopy was used to study the photolysis of HX (X=Cl, Br, I) adsorbed on LiF(001). Adsorption characteristics were investigated by temperature programmed desorption. While HCl and HBr appeared to form stable but perforated monolayers on LiF(001), HI did not wet the surface under equilibrium conditions. This behavior of HI was ascribed to the mismatch of its van der Waals diameter and the spacing of the adsorption sites on the substrate lattice. The photolysis experiments were performed with 193 nm excimer laser radiation incident on submonolayers at low temperatures (30–60 K). The H-atom translational energy distributions, P(ET′), showed a marked decrease in the fraction of H-atoms scattered inelastically in going from HCl(ad) to HBr(ad), followed by a similar increase in going from HBr(ad) to HI(ad). These nonmonotonic changes in PINEL down the series HX(ad) (X=Cl, Br, I) were thought to be due to the opposed effects of decreasing adsorbate density (which decreases PINEL by reducing the probability that recoiling H(harpoon above, rightward) encounters a neighboring HX(ad)), and increasing collision energy (which increases PINEL). At H-atom energies of ET(approximate)3.3 eV vibrational structure in the H-atom translational energy distribution, P(ET′), following photolysis of HI(ad) gave evidence of efficient T→V energy transfer to neighboring adsorbate molecules. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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