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  • 1
    Electronic Resource
    Electronic Resource
    Surface effect-induced fast Be diffusion in heavily doped GaAs grown by molecular-beam epitaxy (1986)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 60 (1986), S. 201-204 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: van der Pauw measurements, C-V measurement, and secondary ion mass spectrometry were used to study the rapid diffusion of Be in heavily doped GaAs epilayers grown by MBE. The concentration dependence of the Be diffusion was measured. A discrepancy exists at high doping level between our experimental results and the Be interstitial-substitutional diffusion model previously proposed. The threshold of fast Be diffusion versus doping concentration was determined and a diffusion coefficient as high as 2×10−12 cm2/s was observed at 600 °C. A surface Fermi-level pinning effect model has been proposed in addition to the interstitial-substitutional model, which has successfully explained the onset of fast Be diffusion in MBE-grown GaAs at high doping level.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.337681
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  • 2
    Electronic Resource
    Electronic Resource
    On the different representations of the hole-correlation functions in the Hartree–Fock and the Hartree–Fock–Slater methods and their influence on bond energy calculations (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 8051-8060 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have investigated the change in shape of the Hartree–Fock Fermi-hole correlation function upon bond formation. Our analysis indicates that the molecular Fermi-hole correlation function is on the whole considerably more diffuse than its atomic counterpart. It is shown that this imbalance gives rise to HF bond energies which in many instances are much smaller than the experimental values. The imbalance is related to the so-called near degeneracy error, a well known feature of the HF method. It can be removed by introducing a limited configuration interaction calculation which ensures a proper dissociation limit as the bond is broken. The Fermi-hole correlation function adopted by the Hartree–Fock–Slater method does not introduce the same imbalance between molecular and atomic hole functions. The calculated bond energies are, as a consequence, much larger and in better agreement with experiment. It is suggested that the Hartree–Fock–Slater method in part introduces correlation by avoiding the near degeneracy error through a balanced description of the molecular and atomic hole functions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459335
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  • 3
    Electronic Resource
    Electronic Resource
    NH2 electron affinity (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 2762-2763 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The 363.8 nm (3.408 eV) photoelectron spectrum of the NH2 (X˜ 2B1)+e−←NH−2(X˜ 1A1) transition of the amide anion is reported. The electron affinity of amidogen is found to be EA(NH2) =0.771 ±0.005 eV. P, Q, and R rotational branches are observed in the spectrum; a simple model which accounts for the band structure is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456994
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  • 4
    Electronic Resource
    Electronic Resource
    Vibrational and electronic spectroscopy of pyridine and benzene adsorbed on the Rh(111) crystal surface (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 441-450 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report the vibrational and electronic spectra for pyridine and benzene adsorbed on the Rh(111) crystal surface obtained by high-resolution electron energy loss spectroscopy (HREELS). Low-energy electron diffraction (LEED), thermal desorption spectroscopy (TDS), and optical second harmonic generation (SHG) have also been used to provide complementary information. Pyridine adsorption on Rh(111) was studied over the 77–450 K temperature range. At 77 K, multilayers of pyridine are observed with a vibrational spectrum similar to that of liquid pyridine. Between 185 and 230 K, HREELS and TDS indicate that both physisorbed and chemisorbed pyridine species are present on the surface. The physisorbed species desorbs at 295 K, while the chemisorbed species is stable until it decomposes on the surface at 400 K. We propose that the chemisorbed species is an α-pyridyl complex as thermal desorption spectroscopy indicates partial dehydrogenation of this pyridine surface species. Electronic energy loss spectra for both benzene and pyridine adsorbed at 310 K show only a weak transition centered at ∼4 eV. The absence of prominent π→π* transitions, which are readily observed for multilayers of benzene adsorbed on Rh(111), implies that the π orbitals are strongly involved in the chemisorption bond of these molecules with the Rh(111) surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454622
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  • 5
    Electronic Resource
    Electronic Resource
    Vibrationally excited O2 in flames: Measurements on v‘=9–11 by laser-induced fluorescence (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 2500-2504 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Vibrationally-excited ground state O2 is detected in a CH4/O2 flame in levels v‘=9–11 by laser-induced fluorescence in the B 3Σ−u–X 3Σ−g Schumann–Runge system. Accurate line positions are measured by calibration against OH(A–X) lines appearing in the same spectra. Signal levels indicate that measurements up to at least v‘=18 should be practical in such flames. The absolute energies of the three vibrational levels agree very well with RKR calculations of Albritton, based on earlier experimental work, but there is substantial disagreement for v‘=11 with the extensive data of Creek and Nicholls.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452101
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  • 6
    Electronic Resource
    Electronic Resource
    Photoelectron spectroscopy of BH−3 (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 795-806 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have studied the photoelectron spectra of BH−3 and BD−3 and have measured the electron affinities of borane; we find EA(BH3)=0.038±0.015 eV and EA(BD3)=0.027±0.014 eV. The peak splittings and intensities demonstrate that the BH−3 ion and the BH3 neutral have very similar geometries; our spectra are consistent with a planar structure for both species. Variational calculations of a coupled oscillator basis over an ab initio potential give an excellent fit to the experimental frequencies and photodetachment Franck–Condon factors. This ab initio model leads to equilibrium geometries with both BH3 and BH−3 as planar molecules with re(BH−3) =1.207 A(ring) and re(BH3)=1.188 A(ring). We find ΔH(open circle)f0(BH−3) =23.1±3.8 kcal mol−1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456104
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  • 7
    Electronic Resource
    Electronic Resource
    Emission spectroscopy of the predissociative Rydberg B state of CH3I and CD3I at 193.3 nm (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 3463-3469 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We measured the emission spectra of CH3I and CD3I excited to a predissociative Rydberg state (E,1){2} near 193.3 nm and tabulated emission line positions with their assignments. The emission spectrum of CH3I both provides previously unobserved energies of ground state combination bands in ν2 (CH3 umbrella) and ν3 (C–I stretch), and also suggests the excited level in the (E,1){2} Rydberg state is the previously unobserved 2132 state. These results are discussed in relation to recent comparisons of UV absorption spectra of monomeric and dimeric CH3I. The CD3I emission spectrum measured results from excitation of the combination mode of CD3 rocking (ν6), umbrella motion (ν2), and C–I stretching (ν3) in the (E,1){2} rydberg state of CD3I, followed by emission to a progression of 2n3161 combination modes in the ground electronic state. A simulation of the line shape of the peaks in the CH3I spectrum shows the width of the peaks results from the contribution of both inhomogeneous (K and J rotational structure) and homogeneous (lifetime) broadening. Emission from molecules after crossing to the repulsive surface was not observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454916
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  • 8
    Electronic Resource
    Electronic Resource
    The determination of molecular structures by density functional theory. The evaluation of analytical energy gradients by numerical integration (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 322-328 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An algorithm, based on numerical integration, has been proposed for the evaluation of analytical energy gradients within the Hartree–Fock–Slater (HFS) method. The utility of this algorithm in connection with molecular structure optimization is demonstrated by calculations on organics, main group molecules, and transition metal complexes. The structural parameters obtained from HFS calculations are in at least as good agreement with experiment as structures obtained from ab initio HF calculations. The time required to evaluate the energy gradient by numerical integration constitutes only a fraction (40%–25%) of the elapsed time in a full HFS-SCF calculation. The algorithm is also suitable for density functional methods with exchange-correlation potential different from that employed in the HFS method.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454603
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  • 9
    Electronic Resource
    Electronic Resource
    The application of density functional theory to the optimization of transition state structures. I. Organic migration reactions (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 3645-3652 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present here the first determination of transition state structures based on Hartree–Fock–Slater (HFS) density functional calculations. The optimization of the transition state structures utilized the analytical energy gradients evaluated by a recently developed method. The transition state structures obtained by the HFS method are similar to those determined by ab initio methods in which electron correlation is partly taken into account. The energy barrier for the CH3NC→CH3CN isomerization process, corrected for the zero-point energy, is 40.1 kcal mol−1 which is in good agreement with the experimental value of 38.4 kcal mol−1. Experimental barriers are not available for the HNC→HCN and N2H2(trans)→N2H2(cis) isomerization processes. However, the barriers calculated by the HFS method are in good accordance with the barriers obtained from electron-correlation calculations. Furthermore, the vibrational frequencies calculated by the HFS method are in good agreement either with experiments in the case of stable molecules or with electron-correlation calculations in the case of transition states. The HFS method seems in general to provide better estimates of vibrational frequencies and activation barriers than the Hartree–Fock method in which electron correlation is lacking. The later method generally afford too high values for both frequencies and activation barriers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457820
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  • 10
    Electronic Resource
    Electronic Resource
    A temperature dependent simulation of the x-ray powder spectrum of ice Ih using Metropolis Monte Carlo sampling (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 4660-4666 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this study we simulate the temperature dependence of powder x-ray diffraction for ice Ih using a model ice sample and Metropolis Monte Carlo simulations. We permit the water molecules to interact through the revised central force potentials of Stillinger and Rahman [J. Chem. Phys. 68, 666 (1978)]. The model ice sample is a periodic unit cell possessing 192 water molecules which are arranged in their initial configuration to yield very small point dipole and quadrupole moments [J. Chem. Phys. 78, 5103 (1983) and J. Phys. Chem. 87, 4309 (1983)]. We report the x-ray powder simulations for input temperatures of 100, 200, and 260 K, comparing them with earlier work at 20 K. A full set of the corresponding structure factors is computed for 300 K. The results suggest a monotonic decrease in the logarithm of the diffraction intensities with increasing temperature and an abrupt change between 260–300 K. The drastically decreased values at 300 K are consistent with previous related work [J. Phys. Chem. 87, 4309 (1983)]. The results are compared with the literature on related x-ray measurements [Nature 188, 1144 (1960)]. Here we comment on the qualitatively good comparisons between experiment and simulation, we note quantitative differences between experiment and simulation, and we discuss the differences in light of limitations in both experiment and theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451763
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