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  • 1
    Electronic Resource
    Electronic Resource
    On the genus of varieties of condimension 2 in projective space (1983)
    Springer
    Mathematische Annalen 265 (1983), S. 115-117 
    Details
    ISSN: 1432-1807
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01456940
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  • 2
    Electronic Resource
    Electronic Resource
    On the potential energy surface for collinear OH+2 (4Σ−) (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 3774-3777 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The potential energy surface for collinear OH+2 (4Σ−) has been investigated at the configuration interaction (CI) level using large primitive basis sets of Gaussian type orbitals (GTO) and the general atomic natural contraction (ANO). The CI calculations were carried out using the CIPSI algorithm and the accuracy established by comparison with full CI (FCI) test calibrations on the atoms and molecules of interest in the present work. For the reaction O+(4Su)+H2(1Σ+g)→OH+(3Σ−)+H(2Sg) the calculated value for the energy change of the reaction (ΔE) is −0.30 eV to be compared with an experimental value of −0.45 eV. The error in ΔE arises from the error in the ionization potential of oxygen and does only affect the reactants but not the products, while the discrepancy with the experiment is limited by the finite size of the basis set and not by truncations on the CI expansion. The collinear OH+2 minimum has been found to lie 0.338 eV below the products with an estimated accuracy of 0.01 eV.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459749
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  • 3
    Electronic Resource
    Electronic Resource
    Ab initio, variational transition state theory and quasiclassical trajectory study on the lowest 2A′ potential energy surface involved in the N(2D)+O2(X 3Σg−)→O(3P)+NO(X 2Π) atmospheric reaction (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 2530-2539 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A CASSCF and CASPT2 ab initio study has been carried out for the lowest 2A′ potential energy surface (2 2A′ PES) that correlates reactants and products of the N(2D)+O2→O(3P)+NO reaction. All the stationary points have been characterized and along with a grid of more than 600 ab initio points have been fitted to an analytical function. Afterwards, this analytical PES has been employed to study the kinetics [variational transition state theory (VTST) and quasiclassical trajectory (QCT) methods] and dynamics (QCT method) of the reaction. Concerning the rate constants, a good agreement with the experimental values corresponding to the global deactivation of N(2D) has been obtained. This suggests that this reaction is responsible of most of the reactivity of the N(2D)+O2 system. NO vibrational distributions have also been calculated. Although there is not a good agreement between the theoretical and experimental values, preliminary results show that they can become quite close by taking into account the contribution of the 1 2A″ PES. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1385151
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  • 4
    Electronic Resource
    Electronic Resource
    A theoretical approach to the O(1D)+H2O(X 1A1) reaction: Ab initio potential energy surface and quasiclassical trajectory dynamics study (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 6736-6747 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An ab initio study of the ground potential energy surface (PES) of the O(1D)+H2O system has been performed, employing Møller–Plesset methods. From the stationary and additional points calculated, the ground PES has been modeled as a triatomic system, with an OH group of the H2O molecule treated as a single atom of 17.0 amu. The rate constant of reaction (1), O(1D)+H2O→2OH (main reaction channel), estimated from the quasiclassical trajectory (QCT) calculations is reasonably close to the recommended experimental value. For the relative translational energies explored (ET=0.234, 0.303, and 0.443 eV) and H2O at T=300 K, the QCT OH vibrational populations are in good agreement with the experimental values reported for the new OH fragment, but the QCT OH average rotational energies are in general quite larger than the experimental ones. Regarding the stereodynamics, for ET=0.234 eV there is not a clear tendency to a particular rotational alignment of the OH product with respect to the initial relative velocity vector, in agreement with experiments. The QCT results also show that nearly all reactive trajectories leading to reaction (1) take place through an insertion microscopic mechanism, which, even at the highest ET value considered (0.443 eV), is mainly (70%) a nondirect one. The collision complex has an average lifetime of about three rotational periods and a geometry around that of the HO(OH) hydrogen peroxide molecule. The QCT results concerning the microscopic mechanism of reaction (1) are in agreement with the suggested ones by the experimentalists to interpret their results. The present study should be considered as a starting point in the study of reaction (1) from which different aspects on the dynamics may be learned. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1311295
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  • 5
    Electronic Resource
    Electronic Resource
    Theoretical study of the dynamics, stereodynamics, and microscopic mechanism of the O(1D)+CH4(X 1A1)→OH(X 2Π)+CH3(X 2A2″) reaction (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 6748-6759 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A previously reported potential energy surface (PES) and a new barrierless PES (both based on ab initio data and describing the CH3 group as a pseudoatom) were used to study the O(1D)+CH4→OH+CH3 reaction with the quasiclassical trajectory (QCT) method. The new PES accurately reproduces the experimental rate constant values, in contrast to the previous PES. The QCT study was mainly performed at the relative translational energy (ET) resulting from the photodissociation of N2O at 193 nm (〈ET〉=0.403 eV), although the collision energy obtained from the photodissociation of O3 at 248 nm (〈ET〉=0.212 eV) was also considered. Good agreement between theory and experiment was obtained for the OH vibrational populations and for the OH rotational populations for the v′≥2 vibrational levels, while the rotational distributions for v′=0–1 are more excited than in the experiment. The QCT results at ET=0.403 eV satisfactorily reproduce the experimental kk′ angular distribution of the state-specific channel OH(v′=4, N′=8) and the corresponding ET′ distribution. For OH(v′=0, N′=5) the reproduction of these properties is poorer, especially for the ET′ distribution. At 0.403 eV the contribution of the abstraction mechanism to the reaction mode is negligible and two insertion like mechanisms (with fast or slow elimination) are found to be predominant, as suggested experimentally. The discrepancies observed between the QCT and experimental results can be explained on the basis of the defective description of the insertion/slow elimination mechanism provided by the model. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1289823
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  • 6
    Electronic Resource
    Electronic Resource
    The lowest doublet and quartet potential energy surfaces involved in the N(4S)+O2 reaction. I. Ab initio study of the Cs-symmetry (2A′, 4A′) abstraction and insertion mechanisms (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 1287-1297 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this work we have carried out ab initio complete active space self-consistent-field (CASSCF) calculations, second-order perturbation calculations based on CASSCF wave functions (CASPT2), uncontracted multireference configuration interaction calculations, and some density functional calculations with standard correlation-consistent Dunning basis sets and atomic natural orbital basis sets on the lowest 2A′ and 4A′ potential energy surfaces involved in the title reaction. The ground 2A′ surface has an average energy barrier of 5.3 kcal/mol in the CASPT2 complete basis set limit. A peroxy NOO minimum is found in agreement with preceding ab initio works, which seems to play an important role in the opening of a double microscopic mechanism: direct Cs abstraction and indirect Cs insertion through the NO2(X 2A1) molecule. The ground 4A′ surface shows an average energy barrier of 13.5 kcal/mol in the CASPT2 complete basis set limit. Despite this excited surface displays another peroxy minimum, in this case only a direct Cs-abstraction mechanism can be expected. The present results improve previous high quality ab initio studies and provide lower energy barriers in both potential energy surfaces, which would produce larger total thermal rate constants in better agreement with experimental data. Finally, it is demonstrated that the N and O 2s electron correlation cannot be neglected as it produces a significant decrease in both energy barriers. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1381012
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  • 7
    Electronic Resource
    Electronic Resource
    Ab initio CASPT2//CASSCF study of the O(1D)+H2O(X 1A1) reaction (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 8828-8837 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ground potential energy surface (PES) of the O(1D)+H2O system was studied with the CASPT2//CASSCF ab initio method. We analyzed the degree of validity of an earlier ab initio study by us that used the Møller–Plesset (MP) method. Both the present CASPT2//CASSCF calculations and the highest level MP calculations (PUMP4//UMP2) showed that the main reaction channel (OH+OH) has no energy barrier along the minimum energy path. This result is consistent with the absence of experimental activation energy. The CASPT2//CASSCF and PUMP4//UMP2 results, however, show important differences, mainly concerning the energy, due to the dominant open-shell singlet character of the ground PES. To make an accurate general description of this system, ab initio calculations using multireference methods like the one discussed here are required. Nevertheless, the earlier PUMP4//UMP2 calculations can be taken as a reasonable starting point for characterizing the ground PES of this system. Moreover, the pseudotriatomic (O(1D)+H–(OH)) analytical potential energy surface derived in the previous work to interpret the experimental results is a reasonable model for describing the O(1D)+H2O→2 OH reaction. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1408298
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  • 8
    Electronic Resource
    Electronic Resource
    Ab initio, VTST, and QCT study of the 1 2A″ potential energy surface of the N(2D)+O2(X 3Σg−)→O(3P)+NO(X 2Π) reaction (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 8838-8851 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An ab initio study based on the CASSCF (Complete Active Space Self-Consistent Field) and CASPT2 (Second-Order Perturbation Theory on a CASSCF wave function) methods has been carried out on the ground 2A″ potential energy surface (PES) involved in the relevant atmospheric reaction between N(2D) and O2 to produce O(3P) and NO. Also, some intersections between PES have been studied. The stationary points have been characterized and a grid of more than 800 points have been fitted to an analytical function. This analytical representation of the PES has been used to obtain kinetic and dynamic properties of the reaction. The rate constant of this reaction has been calculated at different levels of theory [variational transition state theory (VTST) and quasiclassical trajectory (QCT) methods] and has been compared with the experimental values (overall rate constant including physical electronic quenching) obtaining a good agreement. The QCT method has also been employed to study the properties of products from both the abstraction and insertion microscopic mechanisms. The vibrational distribution of NO arising from the reaction at 100 K has also been calculated and compared with the experimental ones. In this case, the agreement between the theoretical and the experimental results is not so good, the experimental vibrational distribution being less excited. Future work is necessary to determine the origin of this difference. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1408301
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  • 9
    Electronic Resource
    Electronic Resource
    A four-dimensional quantum mechanical state-to-state study of the H2+C2H→H+C2H2 reaction (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 9882-9894 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A quantum mechanical approach to treat diatom–triatom exchange processes of the type AB+CDE→A+BCDE is presented. The initial nine degree-of-freedom problem is simplified to a reaction having active only five of such degrees of freedom, which emulates a rotating–stretching AB molecule colliding colinearly with a linear CDE molecule. This model is then applied to study the H2+C2H→H+C2H2 reaction. In the present work, the H2 rotations are treated using the infinite-order-sudden-approximation (IOSA) method, whereas the coupled states (CS or jz) approximation is employed to uncouple the total angular momentum J from internal rotations. Thus, a four-dimensional mathematical analysis is performed, which allows the computation of state-to-state reactive probabilities and cross sections. The bending vibrational levels of the acetylene C2H2 molecule are calculated on the basis of a one single degenerate bending expansion, i.e., just one H (the attacked one) is considered to bend, the remainder being frozen. Present results show that the product acetylene is formed in highly excited vibrational states, particularly if either the reacting asymmetric CH or symmetric C2 stretches are involved. Finally, rate constant results are compared with two other theoretical treatments and with experiments. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1367387
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  • 10
    Electronic Resource
    Electronic Resource
    Ab initio and quasiclassical trajectory study of the N(2D)+NO(X 2Π)→O(1D)+N2(X 1Σg+) reaction on the lowest 1A′ potential energy surface (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 10983-10998 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this work we have carried out ab initio electronic structure calculations, CASSCF/CASPT2 with the Pople's 6-311G(2d) basis set on the ground singlet potential energy surface (1 1A′ PES) involved in the title reaction. Transition states, minima and one 1 1A′/2 1A′ surface crossing have been characterized, obtaining three NNO isomers with the energy ordering: NNO (1Σ+)〈cyclic−C2v NON(1A1)〈NON(1Σg+). Approximately 1250 ab initio points have been used to derive an analytical PES which fits most of the stationary points, with a global root-mean-square deviation of 1.12 kcal/mol. A quasiclassical trajectory study at several temperatures (300–1500 K) was performed to determine thermal rate constants, vibrational and rovibrational distributions and angular distributions. The dynamics of this barrierless reaction presents a predominant reaction pathway (96% at 300 K) with very short-lived collision complexes around the NNO minimum, which originate backward scattering and a similar fraction of vibrational and translational energy distributed into products. At higher temperatures other reaction pathways involving NON structures become increasingly important as well as the N-exchange reaction (3.02% of the branching ratio at 1500 K), this latter in accord with experimental data. It is concluded that the physical electronic quenching of N(2D) by NO should be negligible against all possible N(2D)+NO reaction channels. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1327263
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