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  • American Institute of Physics (AIP)  (5)
  • 2005-2009
  • 1995-1999  (5)
  • 1975-1979
  • 1
    Electronic Resource
    Electronic Resource
    Far-field emission narrowing effect of microdisk lasers (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 2223-2225 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Far-field intensity distribution of semiconductor microdisk lasers is experimentally measured and the emission angle is found to be much smaller than that of a planar source with the same near-field width. In fact the emission angle is determined mainly by the disk radius instead of the disk thickness. A scalar diffraction theory in the cylindrical coordinate is developed to explain such an emission-angle-narrowing phenomenon and numerical calculation based on a vectorial diffraction theory is carried out to explain the measured polarization state. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.121328
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  • 2
    Electronic Resource
    Electronic Resource
    Femtosecond real-time probing of reactions. XXI. Direct observation of transition-state dynamics and structure in charge-transfer reactions (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 6216-6248 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This paper in the series gives our full account of the preliminary results reported in a communication [Cheng, Zhong, and Zewail, J. Chem. Phys. 103, 5153 (1995)] on real-time femtosecond (fs) studies of the transition state of charge-transfer (CT) reactions, generally described as harpooning reactions. Here, in a series of experimental studies in a molecular beam, and with the help of molecular dynamics, we elucidate the microscopic elementary dynamics and the structure of the transition states for the isolated, bimolecular reaction of benzenes (electron donor) with iodine (electron acceptor). The transition state is directly reached by fs excitation into the CT state of the complex Bz⋅I2, and the dynamics is followed by monitoring the product build up or the initial transition-state decay. We further employed the fs resolution in combination with the kinetic-energy resolved time-of-flight and recoil anisotropy techniques to separate different reaction pathways and to determine the impact geometry. Specifically, we have studied: (1) the temporal evolution of the transition state (τ
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472478
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  • 3
    Electronic Resource
    Electronic Resource
    Transition states of charge-transfer reactions: Femtosecond dynamics and the concept of harpooning in the bimolecular reaction of benzene with iodine (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 5153-5156 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We describe an approach for real-time studies of the transition-state dynamics of charge-transfer reactions. An application to the bimolecular reaction of benzene with iodine is reported. The measured 750±50 fs transient growth of the free I atom product elucidates the nature of the transition state and the mechanism for the dissociative charge-transfer reaction. The mechanism is formulated in relation to the impact geometry and the dative bonding, which are crucial to condense-phase and surface reactions, and is supported by molecular dynamics. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470603
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  • 4
    Electronic Resource
    Electronic Resource
    Isomeric structures of the electronically excited acetylene⋅Ar complex: Spectroscopy and potential calculations (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 2850-2862 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Acetylene⋅Ar complex in the S1 state has been characterized through laser fluorescence excitation spectra in the acetylene A˜←X˜, 3n0 (n=0–4) bands region. Two isomeric structures have been determined for the acetylene(A˜)⋅Ar complex from rotational band analysis, even though only one structure was known to exist for the ground state acetylene(X˜)⋅Ar. The in-plane isomer has the Ar atom situated in the molecular plane of the trans-bent acetylene, 3.77 A(ring) from the acetylene center of mass and tilted from the H atoms. The out-of-plane isomeric structure, directly inverted from the rotational constants, has argon 3.76 A(ring) away from the acetylene center of mass and 18° tilted from the C2 rotational axis. This structure is most likely due to large amplitude bending motions away from the equilibrium position which is along the C2 axis. Axis switching effect in the rotational band analysis for both isomers has been examined and found to be negligible. (Formulas for calculating the three-dimensional axis switching angles are detailed in the Appendix.) Three van der Waals vibrational mode frequencies have been determined from the vibrational progressions in the spectra; the stretching fundamental of the out-of-plane isomer is 28 cm−1; the in-plane bending fundamental, and the out-of-plane bending first overtone of the in-plane isomer are 11 and 17 cm−1, respectively.The isomeric structures have been compared with the results from a pairwise-atom potential calculation with parameters transferred from the ones previously derived for C2H4⋅Ar potential calculations. It was found that when the set of parameters that most closely reflects the electronic density distribution in C2H2(A˜) orbitals was used, two potential minima mimicking the two isomeric structures were generated. This potential calculation can even qualitatively reproduce the complex spectral shift induced by the ν3 mode excitation in acetylene. Combining the observed spectral shifts and previous experimental and theoretical studies of acetylene(X˜)⋅Ar, we have estimated the binding energy of the out-of-plane C2H2(A˜)⋅Ar isomer to be 179 cm−1, and that of the in-plane isomer to be 170 cm−1. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470723
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  • 5
    Electronic Resource
    Electronic Resource
    Bimolecular reactions observed by femtosecond detachment to aligned transition states: Inelastic and reactive dynamics (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 7864-7867 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: With fs radical detachment and kinetic energy-resolved time-of-flight (KETOF) mass spectrometry, we are able to study the transition state dynamics of the bimolecular reaction CH3I+I, inelastic and reactive channels; the collision complex is coherently formed (1.4 ps) and is long lived (1.7 ps). We also report studies of the dynamics of I2 formation. Direct clocking of the CH3I dissociation, hitherto unobserved, gives 150 fs for the C–I bond breakage time and 0.8 A(ring) for the repulsion length scale. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472606
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