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  • Articles  (258)
  • American Institute of Physics (AIP)  (258)
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  • 1987  (258)
  • Chemistry and Pharmacology  (258)
  • 1
    Electronic Resource
    Electronic Resource
    Ammonia dimer: Further structural studies (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 6364-6372 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: New experimental results on the structural and dynamical properties of NH3 dimer are reported in this work. J=1–0, K=0 transitions of 14NH3–15NH3, 15NH3–14NH3, ND3 dimer, and ND3–ND2H have been measured at high resolution and 14N electric quadrupole coupling constants are reported for each of these species. The NH3 subunits comprising the dimer are inequivalent. The quadrupole coupling constant associated with the first ammonia subunit eqQ1aa, is measured in 14NH3–15NH3 [−627(8)kHz], in ND3 dimer [−531(15) kHz], and in ND3–ND2H [−991(18) kHz]. For the other subunit, eqQ2aa is reported in 15NH3–14NH3 [892(8)kHz], in ND3 dimer [745(13) kHz], and in NH3–ND2H [1013(18) kHz]. These numbers can be used to estimate the vibrationally averaged polar angles of these isotopomers of NH3 dimer. The result is (including the primary isotopomer) θ1 for 14NH3–14NH3 is 48.6°, for 14NH3–15NH3 is 48.7°, for ND3 dimer is 49.6° and for ND3–ND2H is 45.3°; while θ2 for 14NH3–14NH3 is 64.5°, for 15NH3–14NH3 is 64.3°, for ND3 dimer is 62.6°, and for ND3–ND2H is 65.8°. The remarkable invariance of these values rules out the possibility of large vibrational averaging or tunneling averaging in this system and establishes that the angles θ1=49° and θ2=65° are near equilibrium. The isotope effect in thecomponent of the electric dipole moment along the a inertial axis μa, is shown to correlate well with the trend in polar angles given by the quadrupole coupling constants. The absence of interchange tunneling effects in the observed states of NH3 dimer implies that these states are asymmetrically excited internal rotor states of the complex. These experimental structural results are in disagreement with all previous theoretically determined structures for NH3 dimer except one. A recent electronic structure calculation which incorporates correlation through the coupled pair functional approach (while systematically varying geometry) obtains a compact, asymmetric structure for the dimer in close accord to observations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453466
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  • 2
    Electronic Resource
    Electronic Resource
    Toward a Monte Carlo theory of quantum dynamics (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 1641-1647 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We consider in the present paper an extension of numerical path integral methods for use in computing finite temperature time correlation functions. We demonstrate that coordinate rotation techniques extend appreciably the time domain over which Monte Carlo methods are of use in the construction of such correlation functions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453226
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  • 3
    Electronic Resource
    Electronic Resource
    Raman spectra and phase diagram of fluorine at pressures up to 6 GPa and temperatures between 10 and 320 K (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 3016-3021 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The Raman spectra and phase diagram of fluorine were studied in a diamond-anvil cell up to 6 GPa over the temperature range 10–300 K. The sample slowly reacted with the diamond anvils to form CF4. The vibron frequencies in α-F2 and β-F2, as well as the lattice modes in α-F2, were determined as a function of pressure. No new phases were discovered. The α–β phase boundary can be fit with an equation of the Simon form: Pαβ (GPa)=−0.385(10) +4.80(9)×10−4 Tαβ1.75 (K). The melting curve was established to lie between limiting curves: Puppermelt (GPa)=−0.107+1.01×10−4T1.75melt (K) and Plowermelt (GPa)=−0.140+1.32×10−4 T1.75melt (K).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453700
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  • 4
    Electronic Resource
    Electronic Resource
    Dynamical analysis of lattice mode frequencies, specific heats, sound velocities, and Debye temperature of δ and ε-phase O2 monolayers on graphite (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 2332-2335 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Based upon structural and magnetic properties determined in a previous work, a lattice dynamics calculation of the lattice mode frequencies, dispersion curves, specific heats, sound velocities, and Debye temperature of δ and ε-phase O2 monolayers on graphite is conducted. The calculated lattice specific heat of the δ phase is in good agreement with experiment but, for ε-O2, the predicted results fall between two independently measured sets of data with differences that cannot be presently explained. The predicted sound velocities for different propagation vectors show that both δ and ε-O2 are nearly isotropic, elastically.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453113
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  • 5
    Electronic Resource
    Electronic Resource
    Specific heat of a high-Tc perovskite superconductor YBa2Cu3O8−δ (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 5040-5041 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Specific heat measuremnts on high transition temperature perovskite superconductor were conducted from 5.3 K to 345 K. The sample was prepared by mixing stoichiometric amounts of Yttrium oxide, BaO, and CuO so as to yield a 1:2:3 ratio of metals. T he decrease in specific heat at the transition temperature - 91 K is discussed.(AIP)
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452821
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  • 6
    Electronic Resource
    Electronic Resource
    Electron impact excitation cross section studies of methane and acetylene (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 2750-2764 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have measured the electron impact emission cross sections for CH4 and C2H2 at 200 eV in a crossed beam laboratory system. Included in the study are all vacuum ultraviolet (VUV) emission features from 40 to 200 nm. The features are entirely from the atomic dissociation fragments (C i, C ii, and H). The Lyman series of H is observed to truncate near principal quantum number n=10 due to the long lifetime and to the high kinetic energy of the excited H fragments. The threshold region of the excitation functions has been measured at an energy resolution of 0.2–1.0 eV for the Lyman-α and Lyman-β transitions of H and C i (165.7, 193.1 nm) multiplets; and several distinct appearance potentials (AP) have been detected. For example, appearance potentials of Lyman-α from dissociation of CH4 and C2H2 are noted at several energies, including the first observations of a Lyman-α AP from C2H2 at 16.3 eV.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452077
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  • 7
    Electronic Resource
    Electronic Resource
    The relationship between shape resonances and bond lengths (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 2765-2771 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A discussion is presented on the general nature of shape resonances in small molecules and how they may relate to molecular bond lengths. Criteria for assigning photoabsorption features as shape resonances are described, and the usefulness of photoemission experiments to such assignments is highlighted. Based on these criteria, all unambiguously identified K-shell shape-resonance features in molecules containing B, C, N, O, and F are examined in an attempt to identify empirically a shape-resonance energy/bond length relationship. Although the available data are insufficient to establish a quantitative correlation, they indicate the influence of other variables besides the bond length to the energy position of a shape resonance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452078
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  • 8
    Electronic Resource
    Electronic Resource
    The gas phase infrared spectrum of ν1 and ν1−ν4 HCN---HF (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 1225-1234 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A continuously tunable single frequency color center laser has been used to investigate the rovibrational static gas phase infrared spectra of the ν1 (H–F stretching vibration) and its hot bands ν1+ν17 −ν17 and ν1+ν4−ν4 in the linear dimer HCN---HF. Observed perturbations in the ν1 and ν1+ν17 −ν17 subbands results from Coriolis interactions of the excited vibrational states ν1 and ν1+ν17 with ν2+2ν4+ν17 and ν2+2ν4+2ν07 , respectively. The influence of Coriolis interactions and vibrationally predissociating excited state lifetimes of 1.06(10)×10−10 s are considered in simulation of the observed band profiles. Molecular and anharmonic cross term parameters associated with investigated vibrational states are also presented. Anharmonic crossterms X(open circle)14 , X(open circle)17 , and X(open circle)47 are evaluated as 8.0252(73), 4.2162(53), and 1.000(49) cm−1, from the available data, including the analysis from the unresolved spectra of ν1−ν4 and ν1−ν4+ν17 −ν17 . The differences of the band origins in ν1 and ν1−ν4 give a value of ν4=168.344(21) cm−1 for the local spacing of the low frequency hydrogen-bond stretching vibration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452212
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  • 9
    Electronic Resource
    Electronic Resource
    Absolute state-to-state total cross sections for the reactions N+2(X˜,v'=0–2) +Ar(1S0)→N2(X,v)+Ar+(2P3/2,1/2) (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 170-175 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Absolute state-selected total cross sections σv', v'=0 and 1, for the reaction N+2(X˜,v'=0,1) +Ar(1S0)→N2(X,v)+Ar+(2P3/2,1/2) [reaction (1)] over the center-of-mass collisional energy (Ec.m.) range of 1.2–140 eV have been measured using the photoionization mass spectrometric and radio frequency ion guide methods. These measurements, together with the relative values for σv', v'=0–2, and spin-orbit-state distributions of product Ar+ ions determined using the crossed ion-neutral beam photoionization apparatus, allow the determination of the absolute values for σ2 and partial state-to-state cross sections σv'→J, v'=0–2, for reaction (1). Absolute values for σv', v'=0–2, at Ec.m.=8 and 20 eV are in good agreement with those determined previously by the threshold photoelectron secondary ion coincidence method. Absolute values for σv'→J, v'=0–2, at Ec.m.=8 and 20 eV are also found to be in satisfactory accord with the predictions of the semiclassical multistate calculation which uses the ab initio potential energy surfaces of the [N2+Ar]+ system. Experimental state-to-state cross sections obtained in this study are consistent with those for the reaction Ar+(2P3/2)+N2(X,v=0)→Ar(1S0)+N+2 (X˜,v') from the consideration of microscopic reversibility.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452607
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  • 10
    Electronic Resource
    Electronic Resource
    Direction of the dipole-moment derivative of the O–H stretching vibrations of coupled O–D--O–D pairs in H2O ice Ic (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 7244-7245 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The relative intensity of the in-phase and out-of-phase vibrations of intermolecularly coupled O–D--O–D pairs in ice Ic shows that the dipole-moment derivatives for the O–D stretching vibrations in ice Ic are within about 3° of the tetrahedral lines between water molecules. In the gas phase the dipole-moment derivatives are directed 25° outside the O–D bonds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452330
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