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  • Articles  (28)
  • American Institute of Physics (AIP)  (28)
  • American Physical Society
  • 1990-1994  (28)
  • Chemistry and Pharmacology  (28)
  • 1
    Electronic Resource
    Electronic Resource
    Infrared spectrum of a chemisorbed molecule: Computational aspects, analysis of experimental data for ethylidyne on Pt(111) (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 9167-9179 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A microscopic model is presented for anharmonic vibrations of ethylidyne, 3/4 CCH3, chemisorbed on the Pt(111) surface. The model includes 24 vibrational modes of the adsorbate and of the solid. A quantum-mechanical calculation based on second-order perturbation theory is used to interpret experimental data on vibrations of 3/4 CCH3/Pt(111) and 3/4 CCD3/Pt(111). The measured temperature dependence of the CC infrared fundamental and of the umbrella mode fundamental can be accounted for by anharmonic coupling between the CC stretch and the three PtPt stretch coordinates at the base of the adsorbate. Line shapes calculated using classical molecular dynamics disagree significantly with quantum-mechanical results, the apparent reason being overestimation of vibrational energy transfer in the classical calculation. A semiclassical approximation is suggested, in which all the high frequency adsorbate modes except the infrared absorbing mode are frozen; the remaining modes are treated by classical mechanics. The semiclassical calculation agrees much better with the quantum-mechanical results, and can be extended to higher dimension in a straightforward fashion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459206
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  • 2
    Electronic Resource
    Electronic Resource
    Two-photon induced exciton mediated dissociation of N2O and photomobility of O atoms in crystalline Xe (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 6199-6207 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Two-photon induced access of Xe excitons at 248 nm leads to efficient dissociation of N2O impurities via ionic potentials. The product O atoms are probed via the Xe+O− charge transfer transitions, and the N2O disappearance is probed by infrared (IR) spectroscopy. Charge transfer excitation of O atoms leads to atomic mobility, such that with extensive irradiation a photochemical steady-state is reached between N2O, oxygen atoms trapped in the Xe bulk, and within the same cage as N2. A detailed kinetic analysis of these processes is presented. Among the extracted parameters are the two-photon absorption cross section of Xe at 248 nm, 3.7×10−48 cm4 s, the free exciton migration length, 47 A(ring), and the excitonic dissociation probability of N2O, 0.85. The mobility of photoexcited O atoms is attributed to the topology of electronically excited surfaces which show minima at the ground state cage barriers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463728
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  • 3
    Electronic Resource
    Electronic Resource
    Predissociation of H3 n=2 Rydberg states: Product branching and isotope effects (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 8128-8135 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A translational spectroscopy technique is used to obtain predissociation kinetic energy release spectra from the lowest bound states of H3, 2s 2A'1 and 2p 2A‘2. These H@B|3 states are formed in near-resonant electron capture by 3 keV H+3 in Cs vapor. Their ground rovibrational levels are energetically about 1 eV above the H+H+H dissociation limit, thus all levels can yield both H2+H and the three-body products. The spectra contain both three-body and two-body components and are deconvoluted to obtain the branching ratios. Data obtained from two different ion sources show that the three-body/two-body ratio increases with increased rovibrational energy in the H*3. The results are compared to recent theory and with previously reported ratios from dissociative recombination of H+3. The comparison suggests that the ratio increases monotonically with the total electronic and rovibrational energy in the H@B|3. D*3 predissocation has a similar behavior. The H- and D-atom spectra from the two-body decay of HD@B|2 show that the ejected H atom is strongly favored on a per-atom basis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462315
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  • 4
    Electronic Resource
    Electronic Resource
    Site-selective laser spectroscopy of deuterated SrF2:Er3+ (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 2166-2177 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Laser selective excitation and optical absorption of deuterated SrF2:0.05% Er3+ crystals have revealed eight Er3+ ion centers involving D− ion charge compensation, nine new Er3+–F− centers not associated with D− ions and several approximately cubic symmetry Er3+ centers. In contrast to the trigonal symmetry of the principal F− center, the dominant arrangements in the D− ion charge compensation case are derived from a tetragonal symmetry center. Detailed spectroscopic results for the new centers are presented. Fluorescence polarization ratios are listed for three centers ( J, B, and G1) present in either SrF2:Er3+ or CaF2:Er3+ and crystal-field analyses of these, based on assumed trigonal symmetry, are also reported.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458008
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  • 5
    Electronic Resource
    Electronic Resource
    Infrared studies in free standing crystals: N2O-doped Xe and Ar (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 2224-2228 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Infrared studies in N2O-doped free-standing crystals of Xe and Ar are reported. N2O isolates as monomers in Xe; however, it segregates by clustering in Ar. An anomalous temperature dependence of monomeric absorption intensities is observed in Xe, suggesting a strong guest-host electronic interaction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463113
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  • 6
    Electronic Resource
    Electronic Resource
    Electronic spectroscopy of oxygen atoms trapped in solid xenon (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 2229-2236 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The electronic spectroscopy of oxygen atoms trapped in solid xenon are reported. Excitation of the solid between 220 and 260 nm leads to two main emissions centered at 3.35 and 1.65 eV, both of which arise from the same upper state. The excitations are assigned to charge-transfer absorptions in interstitial Oh sites; the emitting state, which has a lifetime of 227 ns, is assigned to Xe+O−(1Σ+). An avoided crossing between the ionic and covalent 1Σ+ states, and differential solvation of these states, explains the main trends of the spectroscopy of XeO in the gas and condensed phases. Implications regarding ionic and covalent many-body surfaces are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463114
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  • 7
    Electronic Resource
    Electronic Resource
    Amplified spontaneous emission over the XeF(D→X) transition in solid Kr (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 1692-1697 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: XeF doped solid Kr represents a novel solid state exciplex laser. A net gain in excess of 100 cm−1 and a superradiant beam of 5 mrad divergence are observed over the XeF(D→X) transition at 301 nm, when free standing crystals of XeF doped Kr are optically pumped near the XeF(D←X) absorption maximum at 260 nm. Superlinear dependence of gain on pump intensity and low divergence of the amplified beam are taken as evidence for self-focusing. The XeF(D) state is effectively isolated from the lower manifold of charge transfer states in solid Kr, which includes XeF(B,C) and (KrXe)+F−.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459940
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  • 8
    Electronic Resource
    Electronic Resource
    Polarization-resolved (2+1) resonance-enhanced multiphoton ionization spectroscopy of CF3I (6s) Rydberg states (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 4355-4371 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The CF3I(5pπ–6s) Rydberg transitions in the energy range 56 700–64 000 cm−1 are investigated using (2+1) resonance-enhanced multiphoton ionization. The polarization of the two-photon transitions is used to definitely assign the symmetries of the resonant intermediate states. The four allowed electronic transitions in the (5pπ–6s) manifold have been assigned and some vibrational constants in the excited states have been determined. Hot band spectra have been obtained in a supersonic expansion of CF3I through an oven. The upper spin–orbit components (the 2E1/2 ion core states) are perturbed by a dissociative state at approximately 63 000 cm−1, possibly the σ–σ* transition centered on the C–I bond. Density functional calculations have been performed in order to help determine the nature of the perturbing states. Vibronic interactions in the excited states are investigated, and evidence is seen for quadratic Jahn–Teller interactions for ν6 in the lower (2E3/2) spin–orbit state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464997
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  • 9
    Electronic Resource
    Electronic Resource
    Henry's law constant for diatomic and polyatomic Lennard-Jones molecules (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 5662-5667 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Simulation results for the infinite dilution chemical potential of Lennard-Jones dispheres in a Lennard-Jones solvent are reported as a function of bond length at various temperatures and liquid densities. Comparisons are made with hard dispheres at infinite dilution. Predictions from theory of the infinite dilution chemical potential of linear chains of Lennard-Jones spheres in nonspherical and hydrogen bonding solvents are presented. Comparisons of the theory are made with recent simulation results for flexible chains of Lennard-Jones spheres.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464915
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  • 10
    Electronic Resource
    Electronic Resource
    Primitive models of chemical association. I. Theory and simulation for dimerization (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 7939-7952 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The structure and thermodynamic properties of a model of associating particles that dimerize into fused-sphere dumbbells are investigated by MC simulation and by integral-equation theory. The model particles, introduced by Cummings and Stell, associate as a result of shielded attractive shells. The integral equation theories are of two types. The first is an extension of Wertheim's associative Percus–Yevick (APY) equation to the case of the shielded sticky shell model, which is the limiting case of the shielded attractive shell model that can be handled analytically. The second is the extended mean spherical approximation (EMSA) of Zhou and Stell applied to the shielded sticky shell model. In the case of partially associated systems, the EMSA requires as input the equilibrium association constant, which is obtained here using an exact relation between monomer density and a cavity correlation function, together with an equation of state due to Boublik. The structure obtained from the EMSA is in good agreement with the predictions of the MC simulation over a substantial density range that includes liquid-state densities, while the thermodynamic input from Boublik's equation is in excellent agreement with the simulation results for all densities. Predictions of the APY approximation are also in good agreement with the simulation results as long as the density of the system is relatively low or, at high density, when the hard-core volume of a dimer is not substantially less than that of the two free monomers from which it is formed. There is an intermediate density range in which neither integral-equation theory gives correlation functions of high quantitative accuracy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468221
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