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  • American Institute of Physics (AIP)  (6)
  • 1
    Electronic Resource
    Electronic Resource
    Surface-aligned photochemistry: Photodissociation of H2S adsorbed on LiF(001) studied by Rydberg-atom time-of-flight spectroscopy (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 807-814 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Photolysis of H2S adsorbed on LiF(001) was studied by means of hydrogen Rydberg-atom time-of-flight spectroscopy. The H-atom translational energy distributions using 193.3 nm radiation showed three main features: a high energy channel attributed to H atoms escaping the surface without collisions (DIR); a vibrational progression from v=0 to v=5 [EL(v=0) and INEL(v〉0)]; and a low energy channel attributed to multiple inelastic collisions [INEL(2)]. The vibrational progression can be attributed to two concurrent processes: the primary production of vibrationally excited SH in the dissociative event, and a secondary T→V energy transfer between the outgoing translationally hot H atom and a neighboring H2S(ad) molecule. The coverage dependence and angular distribution of the DIR, EL, and the INEL(v〉0) channels has been used to define a minimum set of required H2S(ad) geometries. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481856
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  • 2
    Electronic Resource
    Electronic Resource
    Surface aligned photochemistry: Photodissociation of Cl2 and Cl2(centered ellipsis)Cl adsorbed on LiF(001) (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 9569-9581 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Photodissociation of chlorine adsorbed on a LiF(001) surface at 25–70 K has been investigated by means of angularly resolved resonantly enhanced multiphoton ionization spectroscopy (REMPI). The translational-energy distributions and angular distributions for forming Cl(g) photofragments were determined. Photolysis was performed employing 351 nm radiation, with laser pulse energies of 0.3–1.2 mJ/cm2. A peak in the translational energy of Cl(g) at about 0.4 eV was identified as being due to the direct photodissociation of the Cl2(ad) molecule by 3.5 eV photons. Particular interest attached to the observation of a further channel (termed "A") for photodissociation leading to Cl(g) with translational energy peaking at ∼1 eV and extending to 1.5 eV. The available photon energy renders it highly unlikely that this "high-energy" Cl(g) originates in Cl2(ad). Channel A had the same linear dependence of Cl-atom flux on laser pulse-energy as did the lower energy (0.4 eV) channel, termed "B," but differed from it in exhibiting a slow approach to steady state. It appears that channel A requires the prior build-up of Cl(ad) concentration due to the photodissociation of Cl2. It is proposed that this leads to the formation of a steady-state concentration of Cl2(centered ellipsis)Cl which when photolyzed yields high-energy Cl(g) via channel A. Channel A exhibits a distinctive angular distribution at low coverage and a characteristic Cl*/Cl ratio, as compared with channel B. The suggested mechanism for channel A is Cl2(centered ellipsis)Cl+hν→Cl3*→Cl2•Cl→Cl2+Cl (where* is an electronically excited state and • represents repulsion in the lower electronic state to which Cl3* reverts). This mechanism is interpreted in terms of an extensive diatomics-in-molecules (DIM) model for the trichlorine radical, shown to be in agreement with high level ab initio multireference internally contracted configuration interaction (MRCI) calculations, and consistent with the observations. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481574
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  • 3
    Electronic Resource
    Electronic Resource
    Photoinduced charge-transfer dissociation in van der Waals complexes: Na2⋅⋅⋅(ClCH3)n (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 8628-8630 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462268
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  • 4
    Electronic Resource
    Electronic Resource
    Surface-aligned photochemistry: Photolysis of HCl adsorbed on LiF(001) studied by Rydberg-atom time-of-flight spectroscopy (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 598-605 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.478117
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  • 5
    Electronic Resource
    Electronic Resource
    Photochemistry of adsorbed molecules. XVI. Photolysis of HX (X=Cl, Br, I) adsorbed on LiF(001), by Rydberg-atom time-of-flight spectroscopy (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 3129-3134 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.473055
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  • 6
    Electronic Resource
    Electronic Resource
    Photoinduced charge-transfer dissociation in van der Waals complexes. II. Na2...ClCH3, Na2...(ClCH3)2, and Na...FPh (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 5431-5443 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: van der Waals complexes Nam...(XR)n (R=CH3 and Ph; X=Cl and F) have been generated by crossing a beam of Na with a supersonic jet of halide molecules XR seeded with Ar. The complexes were identified and measured by photoionization time-of-flight mass spectrometry. Tunable visible radiation (530–680 nm) was used to measure the photodissociation spectrum (an "action spectrum'') of these clusters. The peak cross section for photodissociation of Na2...(ClCH3)n (n=1 and 2) was found to be large (∼6 A(ring)2) with its maximum at 635 nm for n=1 and at 615 nm for n=2. These peak wavelengths suggest that the primary route for photodissociation is excitation of the Nam followed by charge-transfer dissociation: Na2...(ClCH3)1,2 + hυ → [Na*2...(ClCH3)1,2]
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464892
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