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  • 1
    Electronic Resource
    Electronic Resource
    A crossed-beam study of the state-resolved integral cross sections for the inelastic scattering of OH(X 2Π) with CO and N2 (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 6508-6518 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: State-resolved cross sections for the inelastic scattering of OH(X 2Π) with CO and N2 have been measured in a crossed molecular beam apparatus over the energy range from 0.5 to 5.5 kcal mol−1. The magnitude and shape of the excitation functions for the same OH final states were virtually independent of the two targets except near threshold. Both spin–orbit conserving and spin–orbit changing transitions have been investigated. Cross sections for spin–orbit changing transitions of large ΔN were approximately the same magnitude as those for spin–orbit conserving transitions. For small ΔN, however, the spin–orbit conserving transitions became more favorable. The Λ-doublet ratio, Π(A')/Π(A‘), in the Π3/2 (F1) manifold differed from unity only for the N2 target for which the ratio became increasingly larger than unity as N' increased. The observed fine-structure effects were nearly the same as those from the corresponding (reverse) reactive collisions, and a close connection between the inelastic and reactive events has been conjectured.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460279
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  • 2
    Electronic Resource
    Electronic Resource
    Fine-structure selectivity in polyatomic reaction products: CN(X 2Σ+,v=0,N=0,1)+O2→NCO(X˜ 2Π3/2, 0010,J,e/f)+O (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 1478-1479 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The reaction CN+O2→NCO+O has been investigated in a crossed-molecular beam experiment at a collision energy of 0.76 kcal/mole. Internal state distributions of the ground state NCO(X˜ 2Π3/2, 0010,J,e/f) products have been measured by laser-induced fluorescence. The rotational excitation is small. There is an observed preference in the population of the K doublet fine-structure states, 1f〉1e, and this preference is even stronger for low J states.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459160
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  • 3
    Electronic Resource
    Electronic Resource
    A crossed-beam study of the state-resolved dynamics of CH(X 2Π) + D2. II. The isotopic exchange channel (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 2443-2459 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The state-to-state integral cross sections for the isotopic exchange reaction of CH(X 2Π) with D2 to produce CD(X 2Π) have been measured in a crossed-beam apparatus by the laser-induced fluorescence method. Two types of measurements were performed: (1) the translational energy dependence of an individual quantum state of the product and (2) the state distribution of the products at fixed and well-defined translational energy. To understand some of the finer details of the reaction dynamics similar experiments were also carried out on the reaction CD(X 2Π) with H2 to give CH(X 2Π). For the isotopic exchange channel, the cross section decreased rapidly with increasing translational energy, signifying a complex formation reaction mechanism. The CD(CH) product rotational level distributions are substantially colder than a statistical expectation and are interpreted as the result of a multiple-impact collision between the receding products in the exit channel. A novel frequency-locking mechanism, similar to that proposed to understand the dynamics of inelastic collisions between CH and D2 (the preceding paper), is suggested to explain anomalous peaks in the product rotational level distribution for the isotopic exchange channel. However, the fine-structure state distributions for the reactive process, which are very different from that for the inelastic channel, cannot be rationalized by conventional interpretation. Some basic concepts about fine-structure selectivity in chemical reactions have been developed. With these concepts, it is conjectured that the fine-structure state distributions of open-shell molecules arising from reactive encounters could provide a "fingerprint'' of the electronic wave function at the transition state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459025
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  • 4
    Electronic Resource
    Electronic Resource
    State-to-state integral cross sections for the inelastic scattering of CH(X 2Π)+He: Rotational rainbow and orbital alignment (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 821-838 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The state-to-state integral cross sections for the inelastic scattering of CH(X 2Π) with He were measured in a newly constructed crossed molecular beam machine. Use of laser-induced fluorescence in an unconventional flux mode of detection provided single fine-structure state specific detection of the products. Two types of measurements were performed to further our understanding of the collision dynamics of open shell systems: (1) the product state distribution at a fixed and well-defined collision energy and (2) the dependence on collision energy of product state-resolved cross sections. A qualitative understanding of the collision dynamics can be obtained by properly factoring out features dependent on the fine-structure states, i.e., effects involving individual Λ-doublet states and features dependent on the rotational level alone, i.e., effects remaining after summing over all four fine-structure states associated with a given rotational quantum number. As for the fine-structure effects, a preferential population of product Λ-doublet states with reflection symmetry Π(A‘) was observed. The physical origin of this observed electronic orbital alignment can be attributed to a quantum interference phenomenon, as detailed in the accompanying paper. At the rotational level, the dominance of rotational rainbow scattering is unambiguously identified from both the existence of dynamical thresholds and a strong correlation between rotational level distributions at fixed translational energy and level specific excitation functions. These effects combined with other experimental observations lead us to visualize the CH+He scattering dynamics in a novel fashion. The collision can be regarded as a series of approximately independent sequential events each mediated by different regions of the interaction potential during the course of the whole encounter.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457134
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  • 5
    Electronic Resource
    Electronic Resource
    A crossed-beam study of the state-resolved dynamics of CH(X 2Π)+D2. I. The inelastic scattering channel (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 2431-2442 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The state-to-state integral cross sections for the inelastic scattering of CH(X 2Π) and D2 to produce rotationally excited CH(X 2Π) product have been measured in a crossed-beam apparatus by the laser-induced fluorescence method. Two types of measurements were performed: (1) the translational energy dependence of an individual quantum state of the product and (2) the state distribution of the products at fixed and well-defined translational energy. For the inelastic scattering channel, the cross sections gradually increased from a dynamical threshold to a broad maximum and then slowly decreased as the translational energy increases. Evidence for multiple-impact rotational rainbows was found and a possible frequency-locking phenomenon between the two receding rotors resulted. Moderate orbital alignment was observed except for the highest rotational levels of the product. By comparing and contrasting the kinematically similar system CH(X 2Π)+He, the influence of a strongly attractive potential energy surface on the inelastic scattering of CH+D2 was inferred. Combining the results of the inelastic scattering and the isotopic exchange channels (the following paper) provide an unprecedented look into the dynamics of collisions between CH(X 2Π) and D2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459024
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  • 6
    Electronic Resource
    Electronic Resource
    The inelastic scattering of 2Π [case (b)] molecules and an understanding of the differing Λ doublet propensities for molecules of π vs π3 orbital occupancy (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 839-848 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The quantum formalism for the scattering of a diatomic molecule in a 2Π electronic state which is well described by Hund's case (b) limit is investigated here. For a particular JFi→J'F'1 transition, quantum interference effects will lead to preferential population of one of the final state Λ doublet levels. The nonstatistical population of final state Λ doublet levels arises from an interference between terms in the expansion of the two electrostatic potential energy surfaces, of A' and A‘ reflection symmetry, which describe the interaction between a molecule in a Π electronic state and a closed-shell partner. The particular Λ doublet level preferred is opposite for molecules of π1 vs π3 electron occupancy. The physical origin of this reversal in the Λ doublet propensity is a direct reflection of the fact that for the former the A' potential surface is more repulsive since the sole π electron lies in the triatomic plane in this case, whereas for molecules of π3 electron occupancy the A' surface is less repulsive than the A‘ surface since for the A' surface only one of the three π electrons lies in the triatomic plane. The magnitude of these Λ doublet propensities is illustrated by calculated cross sections for the CH(X 2Π)–He system using the ab initio potential energy surfaces calculated by the Argonne theoretical group, and these cross sections are compared to those of the crossed molecular study of Liu and Macdonald [J. Chem. Phys. 91, xxxx (1989)]. A similar analysis is carried out for collisions of a molecule of π3 electron occupancy and is illustrated by inelastic collisions of OH(X2Π).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457135
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  • 7
    Electronic Resource
    Electronic Resource
    Reaction dynamics of F+HD→HF+D at low energies: Resonant tunneling mechanism (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 7839-7848 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The complete state-resolved differential cross section σ(v′,j′,θ;Ec), investigated in a crossed-beam scattering study, is presented for the title reaction at six initial collision energies (Ec) which are below or near the barrier energy. At low energies, all reactive flux is gated through a trapped resonance state via a tunneling process. Hence, it serves as a benchmark system for better understanding the reactive resonance phenomenon. In addition to highlighting various resonance fingerprints of experimental observable, the concept of resonant tunneling reaction mechanism is elucidated. Particular emphasis is placed on its distinction from the more conventional transition-state reaction mechanism. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1468880
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  • 8
    Electronic Resource
    Electronic Resource
    Reactive excitation functions for F+p-H2/n-H2/D2 and the vibrational branching for F+HD (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 3633-3640 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Complementary to our recent report on the F+HD reaction, the reactive excitation functions for the other isotopomers are presented. Through analysis of the differential cross section data, the collisional energy dependencies of product vibrational branchings for F+HD are also reported here. Several important conclusions can be drawn from this work. First, the transition-state properties, in particular the barrier height, of this reaction are well-characterized by the SW PES, despite its neglect of spin–orbit couplings. Second, contrary to the theoretical conclusion in recent literatures, an experimental observation is presented which seems to suggest that a resonance may indeed exist for the F+H2 reaction in support of the original interpretation proposed by Lee and co-workers. Third, the vibrational branching for the F+HD→HF+D reaction elucidates another facet of resonance effects in the integral cross sections. Finally, the nonadiabatic reactivity of the spin–orbit excited F*(2P1/2) atom is found to be small, which is in line with the conclusion inferred from a most recent, full quantum mechanical multisurface calculation. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1287840
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  • 9
    Electronic Resource
    Electronic Resource
    Direct determination of the spin-orbit reactivity in Cl(2P3/2,2P1/2)+H2/D2/HD reactions (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 1197-1204 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: By exploiting two different Cl-beam sources and concurrently monitoring the concentrations of the two reagents [Cl(2P3/2) and Cl*(2P1/2)] and the H- or D-atom product, the spin-orbit specific excitation functions of the title reactions were determined. The exceptionally large nonadiabatic reactivity for Cl*(2P1/2)+n-H2, inferred in our previous differential cross section investigation, is now confirmed and quantified. The isotope effects for both the spin-orbit ground and excited reagents are also elucidated. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1378834
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  • 10
    Electronic Resource
    Electronic Resource
    Vacuum ultraviolet photochemistry of CH4 and isotopomers. II. Product channel fields and absorption spectra (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 4146-4152 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In part I of this work the relative velocities and anisotropies of the atomic H and D fragments from methane photolysis at 10.2 eV were measured. In this paper the relative abundance of the methyl and methylene fragments are reported. A complete set of quantum yields for the different photodissociation channels of each isotopomer is obtained by combining the two sets of data. Previously it was found that H atoms are almost four times more likely than D atoms to be ejected; now it is found that hydrogen molecule photofragments are much richer in H atoms than in D. Overall, the heavier D atoms are more likely than the H atoms to remain attached to the carbon atom. An implication for astrophysics is discussed. The VUV absorption spectra of CH4 and CH3D are almost identical both at room temperature and 75 K. There is, as expected, no variation in the absorption spectrum with temperature. Evidence is given that all or almost all of the methylene is produced in the a 1A1 and not in the ground 3B1 state. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1288145
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