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  • 1
    Electronic Resource
    Electronic Resource
    Turbidity of deuterated isobutyric acid and heavy water in the one-phase region near the critical solution point (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 464-469 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have measured the total light scattered from a mixture of deuterated isobutyric acid and heavy water (deuterium oxide, D2O ) near its upper critical solution point. The resulting turbidity was measured in a reduced temperature region 10−6〈t〈10−2, where t=(T−Tc)/Tc and Tc is the critical solution temperature, in a sample close to the critical composition. This completely deuterated mixture near its critical point exhibits similar properties to the undeuterated mixture and the turbidity can be explained using an Ising model. When the critical exponents ν and γ were fixed at the values predicted from renormalization-group theory, the amplitude ξ0 of the correlation length was determined to be 0.343±0.024 nm, while the amplitude of the turbidity τ0 was (3.51±0.03)×10−6 cm−1, which seem consistent with two-scale-factor universality predictions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463592
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  • 2
    Electronic Resource
    Electronic Resource
    Vibrationally enhanced dissociative scattering of NO+(Etrans, v=0–6) on GaAs(110) (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 9476-9479 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A hyperthermal beam of state-selected NO+ X Σ+(v=0–6) ions is scattered on a clean, well-characterized GaAs(110) surface. The threshold for the appearance of scattered O− ions occurs at a collision energy of 25 eV. Vibrational energy proves to be an order of magnitude more effective than translational energy in enhancing the yield in this channel.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463272
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  • 3
    Electronic Resource
    Electronic Resource
    Simplified trajectory method for modeling gas–surface scattering: The NO/Pt(111) system (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 3196-3207 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A model is presented to describe the dynamical processes of trapping/desorption as well as direct and indirect inelastic scattering on single-crystal surfaces. Newton's equations of motion are integrated for a system consisting of a rigid rotor interacting with a slab of 19 surface atoms. The surface atom which is closest to the center of mass of the molecule is permitted to translate only along the surface normal. In turn, this mobile surface atom is harmonically coupled to a microcanonical heat bath consisting of three subsurface atoms. This method is much less computationally intensive than the typical generalized Langevin equation (GLE) approach. Direct comparison is made between the predictions of this model and experiment for the NO/Pt(111) system. In the case of trapping/desorption, the model accurately describes the observed dependence of rotational alignment on rotational quantum number. For the inelastic scattering regime, the model successfully reproduces the degree of rotational excitation and qualitatively accounts for the observed rotational alignment. In addition, the model predicts correlations between final state velocity and final state rotational angular momentum (both direction and magnitude), as well as the effect of molecular orientation and surface impact parameter on the overall trapping probability.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456940
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  • 4
    Electronic Resource
    Electronic Resource
    Rotational population and alignment distributions for inelastic scattering and trapping/desorption of NO on Pt(111) (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 3182-3195 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Rotationally resolved experiments on the NO/Pt(111) system explore the mechanisms of inelastic scattering and trapping/desorption. The rotational dynamics associated with these two regimes are markedly different. A neat supersonic NO beam is scattered at normal incidence from a Pt(111) crystal at 375–475 K. The non-Boltzmann rotational population distribution of the scattered species exhibits considerable rotational excitation beyond the energy available from the incident beam. Thus, a surface vibration to rotational energy transfer mechanism must be operative. The accompanying rotational alignment data reveal that highly excited rotational states exhibit predominantly "cartwheel'' motion. In contrast, rotationally excited molecules that desorb from a 553 K Pt(111) surface show a preference for "helicopter'' motion. The opposite preferences for rotational alignment in the two dynamical regimes provide insight into the anisotropy of molecule–surface interactions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456939
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  • 5
    Electronic Resource
    Electronic Resource
    Critical point shifts in binary fluid mixtures (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 560-563 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An empirical observation is made of an apparent universal shift in the consolute point (Xc=critical composition, Tc=critical temperature) of binary fluid mixtures when the system identity is perturbed. The shift in a "pure'' system's critical point (Xco, Tco) when perturbed becomes (Xc,Tc) which seems to obey (Tc−Tco)/Tco= (Xc−Xco)/Xco. This relation has been observed to hold in a wide range of systems including closed-loop coexistence curves (guaiacol–glycerol–water, or tertiary butyl alcohol in secondary butyl alcohol and water), deuterated systems (methanol–cyclohexane, or isobutyric acid–water), impurities added to methanol–cyclohexane, the molecular weight dependence in polystyrene–methylcyclohexane, and the pressure dependence of methanol–cyclohexane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457439
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  • 6
    Electronic Resource
    Electronic Resource
    An ion detector for imaging two-dimensional velocity distributions (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 1969-1972 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The design and performance of a novel ion detector is described. The detector produces a two-dimensional image which displays the time-of-flight distribution of a pulsed packet of ions. Pulse sequencing within the detector allows for simultaneous mass and velocity resolution of the detected ions. The image capturing hardware combines long-term signal integration with single-ion detection in order to provide a wide dynamic range in ion sensitivity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143313
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  • 7
    Electronic Resource
    Electronic Resource
    Scattering state-selected NO+ on GaAs(110): The effect of translational and vibrational energy on NO− and O− product formation (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 6791-6812 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The scattering of state-selected NO+(X 1Σ+, v=0–6) on GaAs(110) was explored across the hyperthermal energy region. Relative yields and velocity distributions for scattered anionic products NO−(X 3Σ−, v=0) and O−(2P) were measured as a function of the number of vibrational quanta and collision energy for NO+(X 1Σ+, v=0–6) incident on the surface. Facile neutralization along the inbound trajectory forms vibrationally excited NO(2Π) immediately prior to surface impact. Electron attachment to form NO−(X 3Σ−, v=0) occurs near the distance of closest approach between the molecule and surface. With regard to O−(2P) emergence, a collision-induced dissociation mechanism is consistent with the observed 25 eV threshold. Incident vibrational energy is as much as ten times more effective than translational energy in forming O−(2P). This paper represents the first experimental investigation into the effect of vibrational energy on electron transfer and dissociation of ions at surfaces and highlights the unique interplay between translational and vibrational motions in an ion/surface encounter.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467039
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  • 8
    Electronic Resource
    Electronic Resource
    Scattering aligned NO+ on Ag(111): The effect of internuclear-axis direction on NO− and O− product formation (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 4996-5011 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Hyperthermal energy reactions of NO+ with Ag(111) were studied as a function of collision energy and the incident diatom's internuclear-axis direction. Laser photoselection via (1+1') resonance enhanced multiphoton ionization (REMPI) prepared an aligned distribution of NO+(X 1Σ+, Etrans, v=0, J) prior to the molecules impact with the surface. The emergence of scattered O− products was enhanced when NO+ approached the surface with an "end-on'' rather than a "side-on'' orientation. Moreover, the magnitude of the reaction's alignment preference increased with decreasing collision energy. The appearance threshold for O− was approximately 20 eV. Classical trajectory calculations demonstrated that these results are consistent with a collision-induced dissociation mechanism mediated by both vibrational and rotational excitation upon impact. Reorientation of the internuclear axis during the collision drastically affects the simulated dissociation dynamics. No alignment preference for scattered NO− emergence could be discerned from the experiments. As a complement, the angular momentum mechanics are provided to predict the internuclear-axis distribution of ions created via two-photon REMPI. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469550
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  • 9
    Electronic Resource
    Electronic Resource
    Rotational alignment of NO desorbing from Pt(111) (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 5038-5039 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452820
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  • 10
    Electronic Resource
    Electronic Resource
    Coexistence curve of perfluoromethylcyclohexane-isopropyl alcohol (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 588-597 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The coexistence curve of the binary fluid mixture perfluoromethylcyclohexane-isopropyl alcohol was determined by precisely measuring the refractive index both above and below its upper critical consolute point. Sixty-seven two-phase data points were obtained over a wide range of reduced temperatures, 10−5〈t〈2.5×10−1, to determine the location of the critical point: critical temperature=89.901 °C, and critical composition=62.2% by volume perfluoromethylcyclohexane. These data were analyzed to determine the critical exponent β close to the critical point, the amplitude B, and the anomaly in the diameter. The volume-fraction coexistence curve is found to be as symmetric as any compositionlike variable. Correction to scaling is investigated as well as the need for a crossover theory. A model is proposed that describes the asymptotic approach to zero of the effective exponent β, which allows an estimation of the temperature regime free of crossover effects. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471912
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