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  • 1
    Electronic Resource
    Electronic Resource
    Accurate measurement of vibrational transition energies for a wide range of v, J states using CARS spectroscopy of chemical reaction products: spectroscopy of hydrogen from the hydrogen-atom + hydrogen iodide reaction (1988)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 92 (1988), S. 3792-3795 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100324a022
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  • 2
    Electronic Resource
    Electronic Resource
    Atomic scale friction of a diamond tip on diamond (100) and (111) surfaces (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 163-167 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The friction of a clean diamond tip on diamond (111) and (100) surfaces is studied using an ultrahigh vacuum force microscope that simultaneously measures forces parallel and perpendicular to the surface. The 30 nm radius diamond tip is fabricated by chemical vapor deposition. The attractive normal force curve between the tip and surface agrees well with calculated dispersion interactions. The frictional force exhibits periodic features, which on the (100) surface are tentatively associated with a 2×1 reconstructed surface convoluted over an asymmetric tip shape. The (111) surface shows features that cannot be simply related to the surface structure. As the tip is scanned back and forth along a line, the same features are observed in each direction, but offset, suggesting the presence of a conservative force independent of the direction of motion as well as a nonconservative force. The friction is approximately (approximately-equal-to)3×10−9 N independent of loads up to 1×10−7 N.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353878
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  • 3
    Electronic Resource
    Electronic Resource
    Experimental and theoretical study of H+HI→H2+I reaction dynamics at 1.3 eV collision energy (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 2756-2761 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The H2 (v', J') partial reaction cross sections arising from collisions of 1.3 eV H atoms with HI have been measured using coherent anti-Stokes Raman scattering (CARS) spectroscopy. Quasiclassical trajectory (QCT) calculations on a representative potential energy surface have been used to simulate the dynamics of this reaction. Comparison of the QCT and experimental results shows good agreement in average energy disposal, total cross section, and rotational state distributions. The only significant disagreement is in the detailed vibrational state distribution, for which the calculations give monotonically decreasing population with increasing v', while the experimental results show a significant population inversion between v'=0 and v'=1. Based on the QCT-experiment comparison we make suggestions for improving the H+HI potential energy surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462024
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  • 4
    Electronic Resource
    Electronic Resource
    State-to-state dynamics of H+HX collisions. II. The H+HX→HX°+H (X=Cl,Br,I) reactive exchange and inelastic collisions at 1.6 eV collision energy (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 4809-4818 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report measurement of product state distributions for the rotationally and/or vibrationally excited HX formed in collisions of translationally hot H atoms with HX (X=Cl, Br, and I) at 1.6 eV collision energy. The product state distributions are probed after only one collision of the fast H atom, using coherent anti-Stokes Raman scattering spectroscopy. Whether proceeding by inelastic collisions or reactive exchange, the transfer of translational energy to vibrational and rotational energy is quite inefficient in H+HX collisions at 1.6 eV. For all three hydrogen halides only 2–3% of the initial translational energy appears as HX vibration. For H+HCl only 6% of the initial energy is converted to HCl rotational energy, while for H+HBr and H+HI, this percentage is twice as large, 11–12%, but still small. The indistinguishability of the two H atoms involved makes it impossible to distinguish reactive exchange from inelastic energy transfer in these H+HX collisions. However, the difference in rotational energy partitioning for H+HBr and H+HI as compared with H+HCl, suggests that reactive exchange is dominant in the former and inelastic energy transfer dominates in the latter. The total cross sections for the combined energy transfer/reactive exchange do not change much with the identity of X, being 13±3, 11±2, and 11±2 A(ring)2, for H+HCl, H+HBr, and H+HI, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456693
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  • 5
    Electronic Resource
    Electronic Resource
    State-to-state dynamics of atom + polyatom abstraction reactions. I. The H+CD4→HD(v',J ')+CD3 reaction (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 1957-1966 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report measurement of the HD product quantum state distributions and absolute cross section for the H+CD4→HD(v',J')+CD3 reaction at a collision energy of 1.5 eV. The total reaction cross section is small, 0.14±0.03 A(ring)2, making the experimental measurements difficult. The HD quantum state distribution peaks at low J' in both v'=0 and v'=1, the only vibrational states in which product is observed. Very little of the 1.5 eV available energy appears as internal excitation of the HD product molecule, 7% in HD product vibration and 9% in rotation. However, linear surprisal analysis shows that this limited internal energy disposal in the HD product in some ways exceeds that expected statistically, since two of the best-fit surprisal parameters (aitch-thetar=2.9±0.6 for v'=0, aitch-thetar=−1.9±0.5 for v'=1, λv=−2.2±0.6 ) are negative. The HD rovibrational state distribution shows an anomalous positive correlation of product vibrational and rotational excitation. Those molecules formed in the vibrationally excited state, v'=1, have significantly more rotational energy (〈Erot〉=0.17 eV) than those molecules formed in the vibrational ground state, v'=0 (〈Erot〉=0.13 eV). This behavior runs counter to the otherwise universal behavior for direct bimolecular reactions—a negative correlation of product vibrational and rotational excitation. We speculate as to the source of this anomalous energy disposal.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462097
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  • 6
    Electronic Resource
    Electronic Resource
    State-to-state dynamics of H+HX collisions. I. The H+HX→H2+X (X=Cl,Br,I) abstraction reactions at 1.6 eV collision energy (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 4795-4808 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The rotational and vibrational state distributions of the H2 product from the reactions of translationally excited H atoms with HCl, HBr, and HI at 1.6 eV are probed by coherent anti-Stokes Raman scattering spectroscopy after only one collision of the fast H atom. Despite the high collision energy, only the very exoergic (ΔH=−1.4 eV) hydrogen atom abstraction involving HI leads to appreciable H2 product vibrational excitation. For this reaction the H2 vibrational distribution is strongly inverted and peaks in v'=1, with 25% of the total available energy partitioned to vibration. For the mildy exoergic (ΔH=−0.72 eV) reaction with HBr and the nearly thermoneutral (ΔH=−0.05 eV) reaction with HCl, very little energy appears in H2 vibration, 9% and 2%, respectively, and the vibrational state distributions peak at v'=0. However, in all three reactions a significant fraction, 18% to 21%, of the total energy available appears as H2 rotation. All three reactions show a strong propensity to conserve the translational energy, that is the translational energy of the H2+X products is very nearly the same as that of the H+HX reactants. For the reactions with HCl, HBr, and HI the average translational energy of the products is 1.3, 1.7, and 1.7 eV, respectively, and the width of the translational energy distribution is only about 0.5 eV full width at half maximum. The energy disposal in all three reactions is quite specific, despite the fact that this high collision energy is well above the barrier to reaction in all three systems and a large number of product quantum states are energetically accessible. Only a few of these energetically allowed final states are appreciably populated. Although detailed theoretical calculations will be required to account completely for the state specifity, quite simple models of the reaction dynamics can explain much of the dynamical bias that we observe.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456574
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  • 7
    Electronic Resource
    Electronic Resource
    State-to-state dynamics of atom+polyatom abstraction reactions. II. The H+C2H6/C3H8→H2(v',J') +C2H5/C3H7 reactions (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 5746-5757 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The rotational and vibrational quantum state distributions for the H2 products of the H+HR→H2+R reactions (HR=C2H6 and C3H8 ) at 1.6 eV collision energy have been measured using coherent anti-Stokes Raman scattering. Total reaction cross sections have also been determined. For the total cross sections we find 1.5±0.5 A(ring)2 for the ethane reaction and 2.9±0.8 A(ring)2 for the propane reaction. Although several vibrational states are energetically accessible, we observe H2 products only in v'=0 and v'=1, with the majority in the ground vibrational state. The H2 products are on average rotationally cold as well, and 20% or less of the total energy is partitioned to H2 internal energy. However, the quantum state distributions show a positive correlation of H2 product rotational and vibrational energy. That is, the average rotational energy of the H2 in v'=1 is substantially greater than the average rotational energy of the H2 in v'=0. Comparison with state-to-state dynamics results previously obtained for the kinematically and energetically similar H+CD4→HD+CD3 and H+HCl→H2+Cl reactions seems to indicate that this anomalous energy disposal is an intrinsic characteristic of H + alkane hydrogen atom abstraction reactions at high collision energy. We speculate that this anomalous behavior is the result of inelastic encounters between the nascent H2 and alkyl radical products in the reaction exit channel.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462673
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