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  • Articles  (568)
  • Wiley  (295)
  • American Institute of Physics (AIP)  (272)
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  • 1986  (568)
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  • Articles  (568)
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  • 1
    Electronic Resource
    Electronic Resource
    On the question of metallic and superconducting poly(carbon diselenide) (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 4019-4027 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Polymerization of carbon diselenide, CSe2, at 5 kbar and ∼100 °C has been reported to give a metallic (CSe2)n ladder polymer that superconducts near 6 K at 220 kbar pressure. Using a variety of techniques we find that the material synthesized (showing essentially the same x-ray diffraction pattern as previously published) is not (CSe2)n but instead consists of a mixture of free, trigonal Se and an amorphous C–Se polymeric composition consistent with the formula (CSe0.5)n. Interestingly, possibly as a consequence of staged reactions during synthesis, the Se phase consists of a mixture of large, aggregated crystallites (∼600 A(ring) in diameter) melting at ∼220 °C and nonaggregated small crystallites (∼150–250 A(ring) in diameter) showing a broad melting transition with an endothermic maximum at ∼180 °C. Percolation of the C–Se polymeric composition probably provides the high observed electrical conductivity [σ(300 K)≈10–20 S cm−1 and σ(300 K)/σ (8 K)≈2.5] in the presently available samples. The previously reported high pressure superconductivity is probably associated with the free Se phase in the samples, since selenium is a known superconductor in the 6 K and 220 kbar range.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450870
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  • 2
    Electronic Resource
    Electronic Resource
    Observation and analysis of the ν2 and ν3 fundamental bands of the H2D+ ion (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 91-99 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The observation of the high-resolution absorption spectrum of the H2D+ molecular ion in the region 2010–2610 cm−1 in discharges through mixtures of H2 and D2 gases is reported. Two types of tunable monochromatic sources are employed, either a diode laser (in Ottawa) or a difference-frequency laser system (in Chicago), and the sensitivity is improved by using either discharge modulation or Doppler velocity modulation techniques. A total of 66 new lines of H2D+ have been measured and assigned, mostly on the basis of ground-state combination differences, to specific rotational transitions of the ν2 and ν3 bands. These data, as well as the two known microwave lines, are fitted by means of two theoretical models, either an effective Hamiltonian model including a Padé representation of a conventional A-reduced centrifugal Hamiltonian for each vibrational level together with Coriolis and higher rotational interactions between ν2 and ν3, or a supermatrix model in which the matrix of the untransformed Hamiltonian is set up in a large vibration-rotation basis and diagonalized directly. In the supermatrix model most of the vibrationally off-diagonal matrix elements are constrained to values derived from Carney's ab initio calculations, while the ν1 parameters are fitted to the observed lines of Amano. Because of the large number of parameters required in the effective Hamiltonian, the less flexible supermatrix model was valuable as a check of the assignments. The results of these fits make it possible to assign seven of the nine lines reported by Shy, Farley, and Wing in 1981. The observed band origins, ν2=2205.87 cm−1 and ν3=2335.45 cm−1, as well as the rotational constants, are in good agreement with ab initio predictions. With the use of one calculated term value to relate the stacks of levels with even and odd values of K‘a, a table of observed term values of the lower rotational levels of the ground state and the ν2 and ν3 states is constructed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450137
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  • 3
    Electronic Resource
    Electronic Resource
    Charge dependence of chemisorption patterns for transition metal clusters (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 4747-4748 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A method is presented for the measurement of the chemisorptive reactivity of transition metal cluster ions at near room temperature. Similar to a technique introduced previously for neutral clusters [Rev. Sci. Instrum. 56, 2123 (1985)], this cluster ion method utilizes a fast-flow reactor attached to a supersonic, laser vaporization metal cluster source, followed by time-of-flight mass spectral analysis of the cluster ions as a function of reactant concentration. Results are presented for clusters of cobalt and niobium in the 1–22 atom size range for their chemisorptive reactions with CO, CO2, and N2. Both Nb+n and Co+n clusters displayed chemical reactivity that is remarkably similar to that of the corresponding neutral clusters. For both charge states of each metal, CO was found to chemisorb with a rate which varied in a slow, monotonically increasing fashion with cluster size. The chemisorption rate of N2 and CO2, on the other hand, was found to be significantly slower than that of CO and sharply dependent upon the cluster size, this dependency being roughly independent of whether the transition metal cluster had a net positive or neutral charge. Photodissociation measurements of the mass-selected positive ion chemisorption products showed that the desorption energy of these products parallels the relative reaction rate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451753
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  • 4
    Electronic Resource
    Electronic Resource
    Kinetics of condensation in supersonic expansion (Ar) (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 2029-2037 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The temperature and density in an overexpanded jet (Ar) were mapped by the method of characteristics. The kinetics of condensation in the supersaturated gas along the central streamline was analyzed on the basis of four models, subject to previously developed thermodynamic relations which must apply during the homogeneous condensation of any supersaturated vapor. Here we report on detailed dynamic analyses of the rates of cluster growth. Each association: An−1+A1(arrow-right-and-left)An was represented either by a single stabilization step, or by a sequence of two energy removing collisions, for which kinetic parameters based on Lennard-Jones (LJ) potentials were estimated. Coupled differential rate equations (up to 192) were solved, both for cases when the heat of condensation was neglected, and when it was partially or fully distributed throughout the fluid. The distribution of cluster sizes declines exponentially, according to N(n)=A exp(−an)+B exp(−bn), in agreement with generally observed distributions for monatomic species. For source pressures of 3 and 10 atm the condensation process becomes kinetically controlled within a distance downstream somewhat less than twice the aperture diameter. Our calculations indicated that after about three aperture lengths "freezing in'' takes place if the heat of condensation is neglected. When the heat of condensation is distributed (partitioned in one of several plausible ways) freezing in is delayed beyond four aperture diameters. A modest fraction of the nascent clusters retain some of the heat of condensation and remain at a higher temperature than the ambient gas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451147
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  • 5
    Electronic Resource
    Electronic Resource
    Hydrodynamic fluctuations in a chemically reacting fluid (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 2140-2146 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: It is shown that the calculation of the nonlocal in time second moments of hydrodynamic fluctuations in a chemically reacting fluid can be done within the framework of extended irreversible thermodynamics. The results obtained imply that a non-Gaussian noise is associated with the fluctuations of the rate of the reaction and of the diffusive flux. The classical results from linear fluctuating hydrodynamics are recovered as a special case of the general results. For the thermostatic second moment in the fluctuations of the internal energy new terms arise whenever fast variables intervene for their description.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451106
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  • 6
    Electronic Resource
    Electronic Resource
    Spin uncoupling in the 6s Rydberg states of methyl iodide. Rotational subband structure in one-photon absorption (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 2483-2488 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Molecular constants of electronic states, all origins as well as some vibronic bands, derived from the lowest-energy Rydberg configuration of methyl iodide, are reported. Values of the internal angular momentum parameter ζeff, which is a measure of the strength of Coriolis and vibronic coupling, indicate that the spin of the Rydberg electron is effectively uncoupled from the molecular axis in the pure electronic states and that dynamic interactions between electronic, rotational, and vibrational motions completely quench the internal angular momentum in some vibronic levels. It is concluded that the parameters ζeff, as obtained from one-photon absorption spectra, are approximately those of the alternate levels, 2E3/2 and 2E1/2, of the CH3I+ ion-core ground configuration X˜.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451817
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  • 7
    Electronic Resource
    Electronic Resource
    Activated dissociative chemisorption of CH4 on Ni(111): Observation of a methyl radical and implication for the pressure gap in catalysis (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 1693-1694 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451211
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  • 8
    Electronic Resource
    Electronic Resource
    Photodetachment studies of metal clusters: Electron affinity measurements for Cux (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 1681-1688 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Laser photodetachment studies have been performed on silver and copper cluster negative ion beams extracted from a supersonic metal cluster source. This source involves the use of laser vaporization within a pulsed nozzle to prepare the neutral cluster jet, followed by ArF excimer irradiation of the nozzle orifice as the copper clusters emerge into the expansion. Photoelectrons ejected from the aluminum nozzle by the excimer radiation are entrained in the supersonic flow and attach to the neutral copper clusters, producing negative ions which stabilize and extensively cool in the subsequent supersonic expansion. Laser photolysis of mass-selected negative copper cluster ions extracted from this source reveals efficient photodetachment to produce a free electron in the absence of measurable fragmentation. The laser fluence dependence of the photodetachment process at different photon energy permits a rough experimental determination of the electron affinities of copper metal clusters as a function of cluster size for the first time.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451838
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  • 9
    Electronic Resource
    Electronic Resource
    A configuration interaction (CI) procedure for the evaluation of two-photon electronic transition probabilities. Program implementation with application to the A1g→B2u transition of benzene (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 2105-2111 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A CI program is described for the evaluation of two-photon electronic transitions, based on time dependent second order perturbation theory. The expression of the transition amplitudes is obtained by directly solving first order perturbation equations over the CI components, avoiding the second order expression with summation over the full set of the intermediate CI eigenstates. The procedure has been implemented as part of a general CI program for ab initio computations of these properties. To test the program, the relative intensities of the "hot'' vibronic components of the A1g→B2u transition of the benzene molecule have been evaluated on a minicomputer and compared to the experiment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451155
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  • 10
    Electronic Resource
    Electronic Resource
    Study of molecular motions in liquids by electron spin relaxation: Halogenated p-semiquinone anions in alcohols (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 6705-6712 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The p-benzosemiquinone radical anion has served as a model system in numerous electron spin resonance liquid-phase relaxation studies. An inconsistency exists of more than an order of magnitude between measured spin-lattice relaxation times T1e and calculated values based on the spin-rotational mechanism if the rotational correlation time τθ that is required in the calculation is obtained from linewidth measurements. This paper presents a number of experiments designed to contribute to the solution of this problem. The rigid-limit g values of tetrahalogenated benzosemiquinone anions have recently become available, permitting the study of the effect of Zeeman anisotropy in a relatively homologous series of compounds. 13C labeled tetrachlorobenzosemiquinone anion (TSCQ−) has additionally been prepared in order to determine the dependence of linewidth on the 13C nuclear quantum number. Linewidth and continuous wave (cw) saturation measurements have been made from 1.0 to 35 GHz. Saturation-recovery pulse measurements of T1e have been made at 9 GHz. Solvent viscosity and temperature have been varied. It is established that an expression of the form [T−11e=AT/η+B exp(−ΔE/RT)] is required to fit the data in hydrogen-bonding solvents with both terms arising from spin-rotation. Values of τθ were determined in five different ways for TCSQ−. The variation is fivefold in ethanol and tenfold in n-butanol. The discrepancy that motivated the research has not been fully resolved, but the data suggests the existence of an additional line broadening mechanism arising from the superposition of signals from radicals in a distribution of relatively long-lived local environments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451401
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