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  • American Institute of Physics (AIP)  (27)
  • 1990-1994  (27)
  • 1920-1924
  • 1992  (27)
  • 1
    Electronic Resource
    Electronic Resource
    A new approach for laser particle acceleration in vacuum (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 3237-3245 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new approach to laser particle acceleration in vacuum is proposed that incorporates three ingredients: (i) a radially polarized laser beam; (ii) an aligned axicon focus; and (iii) the approximate matching of particle and laser phase velocities. This combination has several important advantages which are discussed. The critical issue in any vacuum acceleration scheme is the inherent backward slippage of the particle relative to the laser beam phase, causing the particles to experience successive accelerations and decelerations. According to the Lawson–Woodward theorem, which applies for fairly general conditions, the net result is no energy gain. It is shown that this theorem does not apply to the present laser particle acceleration scheme, and this is verified by applying an exact solution for the electric field. Indeed, acceleration gradients approaching 1 GeV/m over an interaction length of a few centimeters are predicted for 1013 W laser peak power at 10.6 μm.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351442
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  • 2
    Electronic Resource
    Electronic Resource
    Magnetic interaction between Co layers and Pd layers in Co/Pd multilayers (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 4826-4829 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetic moment of Co/Pd multilayers where the Co layer is one layer thick has been calculated using the discrete variational-Xα cluster method. The moment of the multilayer per Co atom as a function of the number of Pd layers (nPd) shows a maximum at nPd=3. Moreover, it is found that the magnetic moment at the central Pd layer is induced antiferromagnetically for nPd=5. We conclude that the Ruderman–Kittel–Kasuya–Yosida interaction is dominant, rather than the d-d interaction between the central Pd layer and the Co layers, while the d-d interaction is dominant between the other Pd layers and the Co layers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352046
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  • 3
    Electronic Resource
    Electronic Resource
    Observation of torsional motion in the ground-state cation of jet-cooled tolane by two-color threshold photoelectron spectroscopy (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 1649-1654 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: High-resolution threshold photoelectron spectra of jet-cooled tolane (C6H5–C≡C–C6H5) have been obtained by two-color (1+1') resonantly enhanced multiphoton ionization via the S1 state {1B1u(ππ*)}. From the threshold photoelectron spectra, the adiabatic ionization energy has been determined to be Ia = 63 917 ± 3 cm−1 (7.9243±0.0004 eV). A vibrational progression due to torsional motion in the cation ground state was observed up to its fifth quantum level with a fundamental frequency of 54 cm−1, showing small anharmonicity. From these results, we have evaluated the potential barrier height to the torsional motion to be 1980±60 cm−1. The threshold photoelectron spectra obtained via several S1 vibronic levels exhibit dominant peaks due to the Δv=0 ionization transitions. This fact indicates that no significant change occurs in molecular structure upon photoionization with removal of the antibonding π electron from the S1 state. Threshold photoelectron bands arising from formally forbidden odd quantum transitions in the torsional mode were also clearly observed with small intensities. The mechanism of the appearance of such a nontotally symmetric mode is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463153
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  • 4
    Electronic Resource
    Electronic Resource
    Vibrational spectra of aniline–Arn van der Waals cations (n=1 and 2) observed by two-color "threshold photoelectron'' [zero kinetic energy (ZEKE)-photoelectron] spectroscopy (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 6399-6406 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Measurements of mass-selected ion-current and threshold photoelectron spectra of jet-cooled aniline–Arn van der Waals complexes (n=1 and 2) have been carried out with a two-color resonantly enhanced multiphoton ionization (REMPI) technique using a high-resolution threshold photoelectron analyzer developed in this laboratory. From our (1+1') REMPI experiments via the respective excited S1 states, we have obtained photoelectron spectra with well-resolved vibrational progressions due to "low-frequency van der Waals modes'' of the cations; νvdW=16 cm−1 (n=1) and νvdW=11 cm−1 (n=2). From Franck–Condon calculations, we have assigned these low-frequency vibrations to the "van der Waals bending'' of the cations. We have also found that the angles of the van der Waals bonds in the cations are changed by 8.2 (n=1) and 8.8 (n=2) degrees with respect to the S1 states. The adiabatic ionization potentials (Ia) of aniline and the aniline–Arn complexes (n=1 and 2) have been determined as 62 268±4 cm−1 (aniline), 62 157±4 cm−1 (n=1), and 62 049±4 cm−1 (n=2). Their shifts ΔIa are 111 cm−1 (n=1) and 219 cm−1 (n=2) with respect to aniline. Spectral shifts due to complex formation have been observed for a total of 13 ring modes of the cations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462634
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  • 5
    Electronic Resource
    Electronic Resource
    Chemical equilibrium in simple fluids: Solvent density dependence of the dimerization equilibrium of 2-methyl-2-nitrosopropane in argon and xenon (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 3824-3829 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have studied the dimerization equilibrium of 2-methyl-2-nitrosopropane (MNP) at 60 and 35 °C in argon and xenon up to densities about twice the critical density of the solvent. With an increase in the solvent density, the dimerization equilibrium constant at 60 °C decreases in the low-density region, whereas it increases in the high-density region. The inversion of the density dependence occurs around ρr(approximately-equal-to)0.8 in argon and ∼1.4 in xenon, where ρr means the density reduced by the critical density of the solvent fluid. The equilibrium constant in xenon at 35 °C increases with increasing solvent density in the low-density region (ρr〈∼0.5), while it decreases in the medium-density region (0.5〈ρr〈1.5). The equilibrium constant in argon at 35 °C has a similar density dependence to that at 60 °C. The internal energy change for the dimerization shows a large density dependence in the low-density region of xenon, while it changes little with density in argon. The theoretical calculation by the Percus–Yevick (PY) approximation for a simple reaction model gives a poor result for the density dependence of the equilibrium constant, although the temperature dependence of the equilibrium constant is reproduced qualitatively. The calculation for a more realistic model including the molecular anisotropy of MNP suggests that the density dependence at the low-density limit is sensitive to the interaction model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461887
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  • 6
    Electronic Resource
    Electronic Resource
    Energy partitioning in the dissociation reaction Ar3+→Ar2++Ar (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 1022-1027 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Threshold-photoelectron photoion coincidence (TPEPICO) spectra of argon clusters ionized with synchrotron radiation have been observed, and the average kinetic energy of Ar2+, which originates from Ar3+, has been estimated. All the line shapes of the Ar2+ ion observed in the TPEPICO spectra have been appropriately simulated in terms of superposition of a sharp and a broad Gaussian function, where the sharp Gaussian function corresponds to ionization of the argon dimer Ar2. The observed line shapes agree very well with the simulated ones, implying that the excess energy in the Ar3 ionization is thermally or quasithermally partitioned to translational energy of the fragment species. From the average kinetic energies of Ar2+, it has been found that the percentage of excess energy in Ar3+, that is partitioned into the total translational energy of the fragment species, is dependent on the excitation energy. The percentage is slightly less than the value of 40% expected from statistical theory. It has also been found that complete dissociation of Ar3+ takes place in the excess energy range 0.3–1.1 eV.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463281
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  • 7
    Electronic Resource
    Electronic Resource
    Coupled channel treatment of transitions between Na(2P1/2,mj) and Na(2P3/2,mj′) in collision with Na(2S1/2,mj″) (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 7423-7432 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Transitions between the Zeeman substates of Na(3p 2P1/2) and Na(3p 2P3/2) in collision with Na(3s 2S1/2) in thermal energy region are investigated by the close-coupling method. Rotational and spin–orbit couplings are taken into consideration, and potential energy functions generated by a quantum chemical calculation are employed. The cross sections strongly depend on the magnetic quantum numbers of the initial and final states. This dependence qualitatively coincides with an experimental observation in the presence of a weak magnetic field, although the magnetic field is not considered in the present calculation. Total cross section of the transition Na(2P3/2)→Na(2P1/2) is calculated to be 2.7×102 A(ring)2 in good agreement with experiment. The following two mechanisms are found to dominantly contribute to the total cross section: (1) Transitions among the molecular states of Na2, 3Π2u↔3Π1u and 3Π1u↔3Π0u, induced by the spin–rotation coupling, and (2) the transition, 1Σ+0g↔1Π1g induced by the Coriolis coupling.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462392
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  • 8
    Electronic Resource
    Electronic Resource
    A study of phenylacetylene and styrene, and their argon complexes PA–Ar and ST–Ar with laser threshold photoelectron spectroscopy (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 8926-8933 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this work, the molecules styrene (ST) and phenylacetylene (PA), as well as their argon complexes ST–Ar and PA–Ar, have been investigated with (1+1') resonance enhanced multiphoton ionization (REMPI) threshold photoelectron spectroscopy (TES). The first adiabatic ionization energies of ST, PA, ST–Ar, and PA–Ar have been measured as 68 267±5, 71 175±5, 68 151±5, and 71 027±5 cm−1, respectively. For both ST–Ar and PA–Ar, the first photoelectron band shows structure in the lowest frequency van der Waals (vdW) bending mode in the ground ionic state, with νvdW being measured as 15 cm−1 in each case. For each molecule excitation to a particular vibrational level of the S1 state followed by ionization, allows structure in that mode to be observed in the threshold photoelectron spectrum. This has been achieved for three modes in both styrene and phenylacetylene. The experimental ionic vibrational frequencies thus obtained, have been compared with those known for the S0 and S1 states.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463367
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  • 9
    Electronic Resource
    Electronic Resource
    Chemical equilibrium in fluids from the gaseous to liquid states: Solvent density dependence of the dimerization equilibrium of 2-methyl-2-nitrosopropane in carbon dioxide, chlorotrifluoromethane, and trifluoromethane (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 3085-3091 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have studied the dimerization equilibrium of 2-methyl-2-nitrosopropane in carbon dioxide (CO2), chlorotrifluoromethane (CClF3), and trifluoromethane (CHF3) at 60 °C from the gaseous to liquid states. The dimerization equilibrium constants are not monotone functions of the solvent density in all solvent fluids. The density dependence of the equilibrium constant shows two inversions: The equilibrium constants in CO2 and CHF3 increase with increasing solvent density up to ρr(approximately-equal-to)0.3, where ρr is the reduced density by the critical density of solvent, whereas the equilibrium constant in CClF3 shows little dependence on the solvent density in this density region. From ρr(approximately-equal-to)0.3 to about 1.4, the equilibrium constants decrease with increasing solvent density. In the higher-density region, the equilibrium constants increase again. We measured the equilibrium constants in CClF3 and CHF3 at 35 °C, and obtain the density dependence of the equilibrium constant which is almost the same as that at 60 °C. The effects of the temperature and the solvent species on the equilibrium constant are larger in the low-density region than in the high-density region. The differences between the low- and high-density regions suggest that the energetic factor is dominant in the low-density region, and that the packing effect is dominant in the high-density region. The experimental results are qualitatively reproduced by a simple reaction model where two spherical molecules dimerize in a fluid composed of spherical molecules, although the reaction model overestimates the equilibrium constant.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461953
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  • 10
    Electronic Resource
    Electronic Resource
    Coupled diabatic configuration interaction treatment of the O2 B'–X transition including computation of predissociation linewidths, optical f values, and generalized oscillator strengths (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 8314-8323 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ab initio CI (configuration interaction) calculations are carried out for O2 in various 3Σ−u excited states in order to study the avoided crossing that is responsible for the discrete B'–X bands found in the high-energy region of the Schumann–Runge continuum. A diabatic transformation is carried out which allows for the description of nonadiabatic effects in this spectral range. A coupled vibrational treatment is employed in conjunction with the complex scaling technique in order to compute the predissociation linewidths of the B' levels, and these results are found to be in good agreement with experiment, particularly for trends observed between different isotopomers of this system. Optical f values and generalized oscillator strengths (GOS) are calculated for a series of vibrational transitions and are also found to compare well with measured data. The observed finding that the GOS varies quite slowly with K2 for the 0–0 transition, but decreases rather sharply for the 1–0 species is reproduced in the calculations and the behavior of this property for other transitions is predicted.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462335
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