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  • 1
    Electronic Resource
    Electronic Resource
    Initial vibrational level distribution of HCN[X˜ 1Σ+(v10v3)] from the CN(X 2Σ+)+H2→HCN+H reaction (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 4224-4236 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The reaction of the cyano radical (CN) with hydrogen was studied by time-resolved infrared absorption spectroscopy of individual rovibrational states of HCN. The initial vibrational level distribution of HCN(v10v3) was determined by plotting the time dependence of the fractional population of a vibrational level and extrapolating these curves to the origin of time. The experiments were carried out at two temperatures, 293 and 324 K, with similar results. It was estimated that about 50% of the available reaction exothermicity was deposited as vibrational excitation of the HCN product. Surprisingly, the HCN(101) vibrational level received a significant fraction of the observed vibrational population, implying that the CN vibration was not really a spectator bond in the reaction dynamics. Furthermore, the observed HCN(v10v3) vibrations only account for about 27% of the initial HCN population produced in the title reaction. A significant fraction of the product HCN molecules must have been produced with the bending mode excited, likely in combination with the H–C stretch vibrations. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477028
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  • 2
    Electronic Resource
    Electronic Resource
    Rotational and translational energy distributions of CN(v=0,J) from the hot atom reactions: H+XCN→HX+CN(v=0,J), where X=Br, Cl, and CN (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 6689-6699 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dynamics of the reactions of translationally energetic H atoms with BrCN, ClCN, and (CN)2 was studied by determining both the rotational state distribution and the translational energy disposition of the CN product ground vibrational level. The reaction was carried out using H atoms with a most probable translational energy of 92 kJ mol−1. The CN radical was monitored by time- and frequency-resolved absorption spectroscopy using the CN red system (A 2Π←X 2Σ) (2,0) band near 790 nm. Sub-Doppler resolution spectroscopy was used to determine the initial translational temperature of the CN(0,J) product. The fraction of the available reaction exothermicity that appeared as CN(0) rotational energy, fR, for H+XCN→HX+CN was 0.034±0.006, 0.061±0.02, and 0.13±0.007, for X=Br, Cl, and CN, respectively. Likewise, the fraction of the available reaction exothermicity that appeared as relative product translational energy, fT, was 0.52±0.25, 0.52±0.20, and 0.59±0.05, for X=Br, Cl, and CN, respectively. The absolute reaction cross sections for the H+XCN→HX+CN reactions were also measured to be 0.03, 0.02, and 0.3×10−16 cm2 for X=Br, Cl, and CN, respectively. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481243
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  • 3
    Electronic Resource
    Electronic Resource
    Experimental and theoretical determination of the magnetic dipole transition moment for the Br(4p5)(2P1/2←2P3/2) fine-structure transition and the quantum yield of Br(2P1/2) from the 193 nm photolysis of BrCN (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 7821-7831 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The integrated-absorption coefficients of several hyperfine lines of the magnetic dipole allowed transition of the bromine atom, Br, center at 3685.2 cm−1 were measured, and a value for the square of the magnetic dipole transition moment of the Br atom was determined. A theoretical calculation for the magnetic dipole transition moment was also carried out using a relativistic ab initio atomic structure formulation. The theoretical value was in excellent agreement with the value predicted assuming pure LS coupling, and in reasonable agreement with experiment. The Br atom was generated in equal concentration with the cyano radical (CN) by the 193 nm photolysis of cyanogen bromine, BrCN. The CN radicals were titrated by the rapid reaction with C3H8 to generate HCN and a small amount of HNC. Both time-resolved and frequency-scanned infrared absorption spectroscopy were used to monitor the Br, HCN, and HNC species. The photolysis of BrCN at 193 nm produced both the ground state Br(2P3/2) and the spin-orbit excited Br(2P1/2) atoms, and the yield for the production of Br(2P1/2) atoms was measured to be 0.31±0.01. The rate constants for the quenching of Br(2P1/2) by BrCN and C3H8 at 293 K were also determined. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478689
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  • 4
    Electronic Resource
    Electronic Resource
    Experimental measurement of the transition moment for the (2,0) band of the CN A 2Π←X 2Σ+ red system at 789.5 nm (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 6312-6319 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The square of the electronic–vibrational transition moment for the (2,0) band of the cyano radical (CN), A 2Π←X 2Σ+, red system at 789.5 nm has been determined using a direct time-resolved absorption technique. The line strength of the R1(8.5) transition of 12C14N was measured by comparison to the known line strength of the H12C14N(001)←(000) P(8) infrared υ3 fundamental transition near 3.05 μm. The CN radical was created by pulsed-laser photolysis of cyanogen, (CN)2, in a mixture of H2 and (CN)2 in either Ar or He carrier gas at 293 K. Both CN and HCN were monitored by time-resolved absorption spectroscopy during the same photolysis laser pulse. A simple kinetic model was used to relate the two absorption features to each other. The square of the electronic–vibrational transition moment for the A←X(2,0) band was found to be 7.8±1.0×10−38 esu2 cm2 in good agreement with theoretical calculations based on ab initio quantum chemistry methods. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477273
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  • 5
    Electronic Resource
    Electronic Resource
    The initial vibrational state distribution of HCN X˜ 1Σ+(v1,0,v3) from the reaction CN(2Σ+)+C2H6→HCN+C2H5 (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 7966-7982 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The reaction of the cyano radical (CN) with ethane was studied using time-resolved infrared absorption spectroscopy to monitor individual rovibrational states of the HCN product. A method is described that can be used to determine the initial vibrational state distribution at pressures of several Torr. This technique was applied to the title reaction to determine that the vibrational states of HCN(v1,0,v3), where v1, v3=0, 1, and 2, were not directly populated in the title reaction to any significant extent. The initial vibrational energy content of the CN radical was also varied but did not influence the initial population in the HCN vibrational levels probed in this experiment. The time dependence of HCN(v1,0,v3) was followed and interpreted in terms of bimolecular rate constants for vibrational relaxation with ethane. The title reaction is mode specific in its energy disposal in that at least every HCN product appears to have at least one quantum of bending excitation, likely in combination with stretching vibrations. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468995
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  • 6
    Electronic Resource
    Electronic Resource
    Direct measurement of the transition dipole moment of the v3 asymmetric C–H stretching vibration of the CH3 radical (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 2863-2872 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A direct measurement of the transition dipole moment, μ3, of the degenerate v3 in-plane asymmetric C–H stretching vibration of the methyl radical has been made. The measurements were carried out in a flow reactor using laser-photolysis transient infrared absorption spectroscopy. Cyano (CN) radicals (and Cl atoms) were produced by laser photolysis of BrCN (or ClCN) at 193 nm and reacted with methane to give both CH3 and HCN (and HCl). The intensities of 18 rotational lines of the v3 fundamental band were measured relative to the R(8) line of the C–H stretching vibration (v3) of HCN(001←0). The best estimate of the transition dipole moment of the CH3 (00110←0) transition was provided by the measured line intensity for the CH3 (00110←0)rR(3,3) transition and was determined to be μ3=0.0327±0.0021 D. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470499
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  • 7
    Electronic Resource
    Electronic Resource
    The dynamical Renner–Teller effect. III. Rovibronic energy transfer pathways in the NCO(X˜ 2Π)+He system (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 3716-3725 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: As a linear triatomic radical in an electronic state with Λ≠0 bends, the vibrationally excited levels are split as a result of vibronic interactions. This is the well-known Renner–Teller effect. Reported here is the first study of the collision-induced transitions between these Renner–Teller components. It is found that the pathways for these processes are highly selective and their efficiencies, in some cases, can compete with rotationally inelastic collisions. A simple, intuitive argument is presented to underscore the physical mechanisms for this finding. Preliminary, more rigorous theoretical analysis confirms the essential ideas of the proposed interpretations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464049
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  • 8
    Electronic Resource
    Electronic Resource
    The dynamical Renner–Teller effect. II. Rotationally inelastic scattering of NCO(X˜ 2Π,0010)+He (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 978-990 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: State-resolved integral cross sections for the inelastic scattering of the Hund's case (a) radical NCO(X˜ 2Π) by He have been measured in a crossed-beam apparatus. Two different types of measurements are reported: (1) state-resolved integral cross sections at fixed collision energies from 0.94–3.05 kcal mol−1 and (2) the collision energy dependence of state-specific product states for both 2Π3/2 and 2Π1/2 spin–orbit states of NCO(X˜ 2Π,0010). As in a preliminary account of this work for E0=3.74 kcal mol−1 [J. Phys. Chem. 91, 9630 (1991)], herein referred to as part I, dramatically different rotational level distributions were found for spin–orbit conserving or changing collisions. It is argued that this behavior and many other observations on this system are generic to the inelastic scattering of Hund's case (a) 2Π radicals. A conceptual framework to understand these results is elucidated in detail. The direct connection between the experimental observables and the Hund's case classification is made for the inelastic scattering of radicals. This connection can be viewed as a dynamical consequence of the Renner–Teller effect.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463200
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  • 9
    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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  • 10
    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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