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  • 1
    Electronic Resource
    Electronic Resource
    Vibration–rotation transfer in molecular super rotors (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 10947-10951 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The collisional behavior of (X)6Li2 molecules in very high rotational levels of v=0 is considered. Highly efficient vibration–rotation transfer is predicted in these "super rotors" particularly when the conditions for quasiresonant transfer are fulfilled. This requires simultaneous near-resonance in energy and in angular momentum. Values of Δj for which quasiresonant vibration–rotation transfer (QRT) occurs become smaller as initial rotor state increases and transfer is likely to become particularly fast for Δj=2, predicted to occur when ji=130. This behavior is contrasted with the inefficiency of pure rotational transfer within the v=0 level for fast-rotating molecules. QRT will take place for quite cold collisions and thus will provide competition for the spinning-up process used to create the super rotors. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1326072
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  • 2
    Electronic Resource
    Electronic Resource
    Quasiresonant vibration–rotation transfer: A kinematic interpretation (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 7697-7700 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A kinematic interpretation for quasiresonant vibration–rotation collisional transfer (QRT) is outlined based on the angular momentum (AM) theory. QRT provides a particularly stringent test since as rotational AM increases, energy decreases (or vice versa). We demonstrate using velocity-AM plots for (A) 1∑u Li2–Ne that although experimentally spectacular, in kinematic terms it constitutes only a slightly unusual energetic constraint to the linear-to-angular momentum conversion. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480107
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  • 3
    Electronic Resource
    Electronic Resource
    A simple model for product rovibrational distributions in elementary chemical reactions (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 5281-5291 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We explore the application of a simple model of collisional processes, developed initially for inelastic collisions, to the analysis of product rovibrational states in elementary chemical reactions. The model depicts collisional transfer as a process of momentum exchange (predominantly linear-to-angular momentum) and is modified to take account of change in center-of-mass and enthalpy change that accompany reaction. The kinematics of center-of-mass shift derived by Elsum and Gordon [J. Chem. Phys. 76, 3009 (1982)] lead to two limiting cases based on the parameter β. The kinematic extremes alternatively may be specified in terms of the molecular torque arm about which interconversion of linear and angular momentum is effected. This torque arm length approximates to the product bond length when β(similar, equals)0 and the reactant bond length when β(similar, equals)90°. Our approach shares elements in common with the classical kinematic model of Elsum and Gordon but is somewhat simpler and more transparent. The method is shown to give accurate peak values of v, j states of the products of a wide range of elementary reactions for which experimental data is available. Monte Carlo trajectory calculations based on the physical principles described here give excellent fits to experimental v, j distributions in F+I2→IF+I, H+D2→HD+D, and Cl+H2→HCl+H using input data consisting of atomic radii, atomic masses, velocities, and reaction enthalpies. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481098
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  • 4
    Electronic Resource
    Electronic Resource
    Rotational and vibrotational transfer in H*–CO2 collisions: The influence of stereokinematic restrictions (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 9287-9295 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We describe a quantitative angular momentum (AM) model for predicting rotational transfer (RT) and vibrotational transfer (VRT) in collisions between CO2 and hot H atoms. This molecule is important in several contexts, not least as a bridge between the relative simplicity of diatomic molecules and the complexities of polyatomic RT and VRT. We show that for pure RT, an AM constraint dominates but that this changes to a dominant energetic constraint in the case of VRT. The requirement that the (001) vibrational channel be opened simultaneously with the generation of AM imposes special restrictions which effectively limit the trajectories that lead to VRT. The origin of this is a constraint-induced restriction on the effective impact parameter (bnmax) for individual Δj channels and the effect is manifest as reduced probability for populating low Δj channels. In CO2–H* this leads to a shift in the peak of (VRT) Δj probabilities away from zero as found experimentally for the (001) vibrational mode. We report a Monte Carlo trajectory calculation similar to that of Kreutz and Flynn [J. Chem. Phys. 93, 452 (1990)] but predict an exponential-like dependence of pure RT on Δj. For VRT to (001) the constraint-induced restrictions on bnmax are incorporated quantitatively and the vibrational channel-opening velocity is treated as a vector quantity. The results of these calculations are in good agreement with experiment. The underlying mechanism, likely to be general in VRT, is clearly revealed in plots of relative velocity versus rotational AM change. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480030
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  • 5
    Electronic Resource
    Electronic Resource
    Polarization of emission from asymmetric rotors. II. Vector reorientation through intramolecular coupling and inelastic collisions (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 733-743 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report measurements of the linear and circular polarization ratios from fully resolved rotational levels of the asymmetric rotor NH2 populated by collisions with H atoms. The results compare well with a theoretical model that includes the depolarizing effects of intramolecular coupling of rotational angular momentum N to nuclear and to electron spin. These have a very significant influence on fluorescence polarization. The model also incorporates the tilting of the N vector in the molecule frame that occurs when inter-k stack transitions take place. Changes in N vector orientation are described with the aid of the angular momentum sphere, a classical representation of the motion of the N vector in a molecule fixed frame. The theoretical treatment assumes the classically impulsive limit for the collisional interaction with conservation of the m quantum number along the kinematic apse. This description of the fate of the N vector under the influence of intra- and intermolecular interactions allows stereodynamical conclusions to be drawn from experimental observations of fluorescence polarization. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474439
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  • 6
    Electronic Resource
    Electronic Resource
    Polarization of emission in asymmetric rotors. I. The effects of elastic collisions, electron and nuclear spins (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 3477-3484 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report measurements of the linear and circular polarization ratios as a function of rotational state for the asymmetric rotor NH2. This molecule displays fine structure splitting from its unpaired electron and hyperfine structure from coupling with the nuclear spins. We present a theory of polarized emission for this molecule which includes the effects of fine and hyperfine interactions. These have a marked effect on the polarization ratios and are well described by a theory in which the effect of electron and nuclear spin are introduced as time-independent perturbation coefficients. We find that theory predicts different values of polarization ratio according to the manner of coupling of the proton nuclear spins. The best fits to experimental data are obtained when the coupling follows a physically intuitive scheme rather than that usually adopted. When all intramolecular couplings due to electron and nuclear spins are properly accounted for; there is no depolarization that may be attributed to the effect of elastic collisions. Thus, as in the case of diatomic molecules, orientation and alignment show a marked stability to change by collision. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473444
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  • 7
    Electronic Resource
    Electronic Resource
    Dynamical angular momentum models for rotational transfer in polyatomic molecules (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 7945-7952 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We propose a model for collision-induced rotational transfer (RT) in polyatomic molecules based on the angular momentum (AM) sphere, a classical representation of the dynamical motion of the rotational AM vector in the molecular frame. The model develops further that proposed by us [AlWahabi et al., J. Chem. Soc., Faraday Trans. 85, 1003 (1989)] in which RT probabilities are related to the AM gap linking initial and final Nkakc states. The AM sphere representation embodies the full internal motion of the molecule via its effect on the inertial axes and the trajectory of the individual rotational state vectors. In this representation there is no unique AM gap for a particular transition between states of nominally well-defined Nkakc and here we propose and test several models for obtaining the distance in AM space between initial and final trajectories. Models are evaluated from their ability to fit data on NH2–H collisions. We find that even the simplest approximations, such as shortest distance in AM space, give good fits to data sets but the best fits are obtained when both AM trajectory and molecular geometry are averaged over. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468993
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  • 8
    Electronic Resource
    Electronic Resource
    Magnetic optical activity of d .fwdarw. d transitions. Octahedral chromium (III), cobalt (III), cobalt (II), nickel (II), and manganese (II) complexes (1967)
    s.l. : American Chemical Society
    Inorganic chemistry 6 (1967), S. 1614-1625 
    Details
    ISSN: 1520-510X
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ic50055a002
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  • 9
    Electronic Resource
    Electronic Resource
    Intensity as a criterion in assigning electronic transitions in metal complexes (1970)
    s.l. : American Chemical Society
    Inorganic chemistry 9 (1970), S. 1563-1565 
    Details
    ISSN: 1520-510X
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ic50088a053
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  • 10
    Electronic Resource
    Electronic Resource
    Rotational pathways in electronic energy transfer (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 9771-9780 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We analyze rotational distributions from collision-induced atom–diatom electronic energy transfer (EET) experiments in terms of the capacity of the diatomic to dispose of the angular momentum (AM) generated in state-to-state change. Two pairs of systems are chosen as representative of processes broadly categorized as "efficient" or "inefficient" in this regard, namely, Na2–Na, Li2–Li in the former category and N2+–He, CN–Ar in the latter. Note that EET involving electron spin change is not considered here. Using velocity-AM diagrams and quantitative calculations we show the factors that govern the probability of state-to-state transfer in EET are the same as those controlling the outcome of rotational and rovibrational transfer within an electronic state. This suggests that requirements of orbital and rotational AM are of critical importance in providing pathways that allow EET to proceed. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1415464
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