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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 6244-6258 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Multireference perturbation theory with complete active space self-consistent field (CASSCF) reference functions was applied to the study of the valence π→π* excited states of benzene and naphthalene. The eigenvectors and eigenvalues of CASSCF with valence π active orbitals satisfy pairing properties for the alternant hydrocarbons to a good approximation. The excited states of polyacenes are classified into the covalent minus states and ionic plus states with the use of the alternancy symmetry. The present theory satisfactorily describes the ordering of low-lying valence π→π* excited states. The overall accuracy of the present approach is surprisingly high. We were able to predict the valence excitation energies with an accuracy of 0.27 eV for singlet u states and of 0.52 eV or better for singlet g states of naphthalene. Our predicted triplet states spectrum provides a consistent assignment of the triplet–triplet absorption spectrum of naphthalene. For benzene we were able to predict the valence excitation energy with an accuracy of about 0.29 eV. The covalent minus states and ionic plus states exhibit different behavior as far as the electron correlation is concerned. The ionic plus states are dominated by the single excitations but covalent minus states include a large fraction of doubly excited configurations. The covalent minus states always give lower energy than the corresponding ionic plus states. This is true for triplet states. The dynamic σ–π polarization effects introduced by perturbation theory are significant for the ionic plus states while those on covalent excited states are usually of the same order as in the covalent ground state. The enlargement of the active space of the reference functions represents a great improvement of the description of the ionic states. The present approach with the pairing properties has proved to be of great value in understanding and predicting the experimental data of the alternant hydrocarbons. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 6520-6528 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The geometry and relative energy of the seven low-lying electronic states of ozone and the ground state of ozonide anion have been determined in C2v symmetry by the complete active space self-consistent field (CASSCF) and the multireference Møller–Plesset perturbation (MRMP) methods. The results are compared with the photodetachment spectra of O−3 observed recently by Arnold et al. The theoretical electron affinity of ozone is 1.965 eV, which is 0.14 eV below the experimental result of 2.103 eV. The calculated adiabatic excitation energies (assignment of Arnold et al. in parentheses) of ozone are 3A2 0.90 eV (1.18 eV), 3B2, 1.19 eV (1.30 eV), 3B1, 1.18 eV (1.45 eV), 1A2, 1.15 eV (∼1.6 eV), 1B1, 1.65 eV (2.05 eV), and 1B2, 3.77 eV (3.41 eV), respectively. Overall the present theory supports the assignment of Arnold et al. However, the simple considerations of geometry and energy are insufficient to determine a specific assignment of the 3B2 and 3B1 states. The dissociation energy of the ground state of ozone is computed to be 0.834 eV at the present level of theory. The present theory also predicts that none of the excited states lies below the ground state dissociation limit of O3. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 1679-1690 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The performance of Xe*2 as a 172-nm fluorescence or laser source when pumped by a low-current, long-pulse electron beam was determined. The fluorescence efficiency of Xe@B|2 is near the theoretical limit of ∼50% at modest pressures over a range of pump rates up to 106 W/cm. The laser efficiency is limited to values 〈1% by a very strong medium absorption that is probably due to Xe*2 photoionization. Laser performance is further degraded by early pulse termination that appears related to mirror degradation. An improved kinetics and extraction code was developed to model the performance of the Xe@B|2 system. A key component of the model is a more detailed treatment of the interactions between secondary electrons and excited atomic and molecular xenon states. Rates for these processes were derived as described herein. With this model, good absolute agreement was obtained between experiments and calculated parameters at pressures as low as 0.5 atm.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 2466-2474 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new type of low-energy ion accelerator has been developed. It includes an eight-storied Disktron generator, newly developed accelerating tubes which hold up to 4 MV/m, both single and tandem acceleration capability, and a compound negative ion source. The Disktron generates 3.2 MV with a dummy load and 2.2 MV with ion beams, and has a voltage stability better than 10−3 at around 1 MV with a corona feedback stabilizer or a generating voltmeter feedback stabilizer only. The highly stabilized voltage of the Disktron has particularly been allowed to form an ion microbeam of about 1-μm diameter.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 135-142 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Intensities of x-ray microbeams formed by the 250-mm-long hollow glass pipes of inner diameters of 27.4, 23.0, and 18.8 μm have been theoretically investigated, by taking account of the slope distribution of microprojections (surface roughness) on the pipe inner wall, using the Monte Carlo method. The intensities for all the pipes calculated on the supposition that each pipe inner wall is perfect (i.e., zero rms of the slope distribution) have been much greater than the experimental values in the x-ray energy region from 6.93 to 19.6 keV. Assuming the slope rms from 2.5×10−4 rad to 3.3×10−3 rad, the calculated results have agreed with the experimental values. Discussions on the results for all the pipes are given in relation to the x-ray anomalous dispersion, the penetration of x rays, the intensity distribution on the x-ray sources used, undulation of the pipes, and the presence of microdust in the pipes.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 1691-1695 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The performance of Kr*2 as a 146 nm fluorescence or laser source when pumped by a low-current, long-pulse electron beam has been determined. The fluorescence efficiency of Kr@B|2 is near the theoretical limit of ∼46% at modest pressures over a range of pump rates up to 3×105 W/cm3. Lasing could not be achieved under the conditions studied here. An improved kinetics and extraction code has been developed to model the performance of the Kr*2 system. A key component of the model is a more detailed treatment of the interactions between secondary electrons and excited atomic and molecular xenon states. Estimated rates for these processes are presented. With this model, good absolute agreement of model predictions with experimental results has been obtained at pressures as low as 0.5 atm.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An amplified spontaneous emission (ASE) from Nd:glass has been introduced into the high power twelve beam Nd:glass laser system, Gekko XII for obtaining smooth intensity distribution of a focused beam. The angular dispersion of an ASE spectrum with large beam divergence was adopted for efficient beam smoothing without significant reduction of the harmonic conversion efficiency. Temporal evolution of the beam smoothing was evaluated as a function of the beam divergence by using a statistical model of speckle. In Gekko XII, the spectral width and beam divergence of ASE were controlled in a range of 0.4 to 0.6 nm and 6 to 22 times diffraction limited, respectively. Final output energy of 1.3 kJ/beam in a 2.2 ns duration was demonstrated without significant gain reduction and spectral narrowing. The doubling efficiency of 50% was obtained at a low intensity region of around 0.3 GW/cm2 by matching the angular dispersion of spectrum to that of phase matching condition of a frequency conversion crystal. The speckle structures in the focused beam pattern measured at the equivalent target plane were greatly smoothed out due to the introduced angular dispersion of spectrum and the large beam divergence. The standard deviation of the intensity distribution of the focused beam pattern was estimated to be 3.3%.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 1871-1876 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: It is demonstrated, both theoretically and numerically, that the Gibbs–Bogoliubov (GB) thermodynamic variational calculation, developed originally for equilibrium systems, can be applied to a thermodynamic metastable system provided the structure of the reference system, used in this calculation, has the same main features as the metastable system under consideration. Following this, the GB thermodynamic variational calculation, employing the hard-sphere system as the reference system, is used to quantitatively determine the thermodynamic features of the metallic glass transition. Good agreement with observation is obtained.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 62 (1991), S. 828-829 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: X-ray microbeams have been produced by utilizing hollow glass pipes. It has been observed that the intensities of ten x-ray lines (from 6.93 to 19.6 keV) transmitted through 250-mm-long hollow glass pipes of inside diameters of 27.4, 23.0, and 18.8 μm range from 1.9 to 2500 times greater than intensities reduced by inverse-square attenuation.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 57 (1990), S. 2876-2878 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The optical grating memory effect in polysilane film is investigated. A refractive index grating is formed within a few minutes by using visible light near room temperature. The grating formation time is dominated by the peak intensity of the pumping beams, and its dependence on the wavelength of the pumping beams corresponds to the two-photon absorption spectrum. The grating formation mechanism is explained as the result of the chain scission induced by two-photon absorption.
    Type of Medium: Electronic Resource
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