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  • American Institute of Physics (AIP)  (15)
  • American Association for the Advancement of Science  (1)
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  • 11
    Electronic Resource
    Electronic Resource
    Photodissociation of water. II. Wave packet calculations for the photofragmentation of H2O and D2O in the B˜ band (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 5787-5808 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A complete three-dimensional quantum mechanical description of the photodissociation of water in the B˜ band, starting from its rotational ground state, is presented. In order to include B˜-X˜ vibronic coupling and the B˜-A˜ Renner–Teller coupling, diabatic electronic states have been constructed from adiabatic electronic states and matrix elements of the electronic angular momentum operators, following the procedure developed by A. J. Dobbyn and P. J. Knowles [Mol. Phys. 91, 1107 (1997)], using the ab initio results discussed in the preceding paper. The dynamics is studied using wave packet methods, and the evolution of the time-dependent wave function is discussed in detail. Results for the H2O and D2O absorption spectra, OH(A)/OH(X) and OD(A)/OD(X) branching ratios, and rovibrational distributions of the OH and OD fragments are presented and compared with available experimental data. The present theoretical results agree at least qualitatively with the experiments. The calculations show that the absorption spectrum and the product state distributions are strongly influenced by long-lived resonances on the adiabatic B˜ state. It is also shown that molecular rotation plays an important role in the photofragmentation process, due to both the Renner–Teller B˜-X˜ mixing, and the strong effect of out-of-plane molecular rotations (K〉0) on the dynamics at near linear HOH and HHO geometries. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481154
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  • 12
    Electronic Resource
    Electronic Resource
    Photodissociation of water. I. Electronic structure calculations for the excited states (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 5777-5786 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Results of ab initio calculations for the four lowest excited states of both A′ and A″ have been discussed. In the multireference configuration interaction calculations, a large Rydberg basis set has been used. Three-dimensional potential energy surfaces, and matrix elements of the transition dipole moment between the excited states and the ground X˜ state, and the electronic angular momentum operator between the A˜ state and the B˜ and X˜ states have been presented. The calculations show that above about 124 nm the photodissociation can be well described by the three lowest electronic states, X˜, A˜, and B˜. The ab initio results of matrix elements of the electronic angular momentum operator allow a realistic nonadiabatic treatment of the photodissociation in the B˜ band. At wavelengths smaller than about 124 nm, the dynamics will be more complicated because of the coupling between various electronic states. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481153
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  • 13
    Electronic Resource
    Electronic Resource
    Photodissociation of CH2. VI. Three-dimensional quantum dynamics of the dissociation through the coupled 2A″ and 3A″ states (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 5757-5770 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present quantitative results on photodissociation of CH2(X˜ 3B1) through the coupled2A′′ and 3A′′ states. A three-dimensional, hybrid quantum dynamical method was used, employing hyperspherical coordinates. The diabatic potential energy surfaces (PES's) used in the dynamics were derived from ab initio calculations. A small product fraction (2.7%) was computed for the CH(A 2Δ)+H channel, in agreement with experiment and approximate dynamical calculations. The dissociation proceeds mostly on a A2-like diabatic surface, into CH(a 4Σ−)+H(93.3%) andC(3P)+H2(4.0%). Resonances of widths in the range 0.1–10 meV affect the photodissociation. Pre-exciting a vibrational mode of CH2(X˜ 3B1) prior to photodissociation does not alter the picture, except if the antisymmetric stretch mode is excited: In this case the product fractions for the C(3P)+H2 andCH(A 2Δ)+H channels collapse to values of 1% or lower, and the resonances disappear. Model calculations show that the large product fraction found for CH(a 4Σ−)+H is due to the initial motion on the "bright"B1-like surface, which biases the outcome of the dissociation in favor ofCH(a 4Σ−)+H. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475130
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  • 14
    Electronic Resource
    Electronic Resource
    The CH+H reaction studied with quantum-mechanical and classical trajectory calculations (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 6002-6011 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The CH+H→C+H2 reaction is studied with quantum-mechanical wave packet calculations and quasiclassical trajectory calculations using a CH2 ground-state potential energy surface. Although quantum tunneling is important for direct hydrogen abstraction, the dominance of the complex formation mechanism ensures the reliability of quasiclassical calculations. Most collisions ((approximate)80%) are nonreactive, because of a too-weak excitation of the CH vibration after a H–CH collision with H approaching CH with HCH angles larger than 60 deg. In this aspect the reaction differs from reactions such as the well-studied O(1D)+H2 reaction, where the H–H vibration in the triatomic complex is strongly excited. Also presented is the rate constant for a temperature range between 50 and 2000 K, obtained from quasiclassical cross-section results for collision energies between 0.0005 and 0.3 eV. The role of the excited triplet and singlet states of CH2 on the reaction dynamics is discussed. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1459416
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  • 15
    Electronic Resource
    Electronic Resource
    Photodissociation of water in the A˜ band revisited with new potential energy surfaces (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 9453-9462 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Theoretical calculations on the photodissociation of water in the first absorption band have been used to test the accuracy of three available potential energy surfaces for the first excited state of water: the well-known coupled electron pair approximation potential of Staemmler and Palma [Chem. Phys. 93, 63 (1985)], and two new multireference double excitation configuration interaction surfaces: the Dobbyn–Knowles surface (unpublished), and the Leiden surface [R. van Harrevelt and M. C. van Hemert, J. Chem. Phys. 112, 5777 (2000)]. Exact quantum mechanical calculations, using the wave packet approach, have been performed for J″〉0, where J″ is the initial rotational state of the water molecule. The cross section was found not to depend strongly on the rotational state, so that it is reasonable to compare calculated cross sections for J″=0 with experimental room temperature cross sections. Small and simple corrections were applied to the potential energy surface to improve the agreement between theory and experiment for the cross section of H2O. Spectra for D2O and vibrationally excited water molecules calculated with all three corrected potential energy surfaces were in good agreement with experiments. A comparison between calculated OH(X) or OD(X) vibrational distributions, and recent kinetic energy release measurements of the H or D atoms produced in the 157.6 nm photodissociation of water and its isotopomers [Yang et al., J. Chem. Phys. 113, 10597 (2000)], however, suggests that the Leiden surface is more accurate than the two other surfaces. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1370946
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  • 16
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    Molecular square dancing in CO-CO collisions (2020)
    American Association for the Advancement of Science
    Details
    Publication Date: 2020-07-17
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science
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