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  • American Institute of Physics (AIP)  (15)
  • 1
    Electronic Resource
    Electronic Resource
    Time dependent thermal lensing measurements of V–T energy transfer from highly excited NO2 (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 4793-4804 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The time dependent thermal lensing technique has been used to measure the vibrational relaxation of NO2 (initially excited at 21 631 cm−1) by Ar, Kr, and Xe. The energy transfer analysis was carried out in terms of 〈〈ΔE〉〉, the bulk average energy transferred per collision. This quantity was found to have a very strong dependence on vibrational energy, with a marked increase at energies greater than about 10 000 cm−1, where several electronic excited states (2B2, 2B1, and 2A2) mix with the ground state (2A1). This effect may be due to large amplitude vibrational motions associated with the coupled electronic states. Even at low energies, deactivation is faster than in other triatomic systems, probably because NO2 is an open shell molecule and electronic curve crossings provide efficient pathways for vibrational deactivation. The V–T rate constant for deactivation of NO2(010) by argon is estimated to be (5.1±1.0)×10−14 cm3 s−1. Results obtained for NO@B|2–NO2 collisions gave 〈〈ΔE〉〉 values in good agreement with literature results from fluorescence quenching experiments, indicating that V–T may be more important than V–V energy transfer in the quenching process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458573
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  • 2
    Electronic Resource
    Electronic Resource
    Reactant states model: Predicted k(E,J) for NO2(2A1)→O(3P)+NO(2Π), based on spectroscopic data (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 2239-2253 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: High-order spectroscopic data for the reactant are used exclusively to determine both the sum of open reactive channels and the density of states, which are used in a statistical theory to predict dissociation rate constants. Practical methods are introduced for calculating sums of reactive channels and densities of states, when couplings among all degrees of freedom are included. An empirical method is described for reconciling spectroscopic parameters with known dissociation energies (also determined spectroscopically). The predicted k(E,J)'s and thermal k∞(T) for NO2 dissociation are in good agreement with experimental data, especially when the effects of electronically excited states are included. The predicted low pressure thermal rate constants are generally in fair agreement with experiment, although a slightly different temperature dependence is calculated; this discrepancy is probably due to the absence of unknown higher order spectroscopic terms and to the crude corrections made for excited electronic states. When high order spectroscopic (or theoretical) data are available and when the effects due to excited electronic states are considered, this theory is useful for predicting, fitting, and interpreting unimolecular rate data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457032
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  • 3
    Electronic Resource
    Electronic Resource
    Energy-dependent collisional deactivation of vibrationally excited azulene (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 6219-6227 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Collisional energy transfer parameters for highly vibrationally excited azulene have been deduced from new infrared fluorescence (IRF) emission lifetime data with an improved calibration relating IRF intensity to vibrational energy [J. Shi, D. Bernfeld, and J. R. Barker, J. Chem. Phys. 88, 6211 (1988), preceding paper]. In addition, data from previous experiments [M. J. Rossi, J. R. Pladziewicz, and J. R. Barker, J. Chem. Phys. 78, 6695 (1983)] have been reanalyzed based on the improved calibration. Inversion of the IRF decay curves produced plots of energy decay, which were analyzed to determine 〈ΔE〉, the average energy transferred per collision. Master equation simulations reproduced both the original IRF decays and the deduced energy decays. A third (simple) method of 〈ΔE〉 determination agrees well with the other two. The results show 〈ΔE〉 to be nearly directly proportional to the vibrational energy of the excited azulene from ∼8000 to 33 000 cm−1. At high energies, there are indications that the 〈ΔE〉 energy dependence may be slightly reduced.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454460
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  • 4
    Electronic Resource
    Electronic Resource
    Energy dependence of infrared emission from azulene C–H stretching vibrations (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 6211-6218 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: New data are described on the energy dependence of infrared fluorescence (IRF) from the C–H stretch modes (∼3050 cm−1) of vibrationally excited azulene (C10H8). An optoacoustic method was used to measure the absorbed laser energy and determine the number of excited molecules, while time-resolved infrared emission was recorded. The experimental uncertainties of ∼5% are much smaller than in previous work and the agreement between the experiments and the theory for the IRF intensity is excellent for total vibrational energies from 14 000 to 33 000 cm−1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454459
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  • 5
    Electronic Resource
    Electronic Resource
    Vibrationally excited populations from IR-multiphoton absorption. I. Absorbed energy and reaction yield measurements (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 6251-6260 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The molecule 1,1,2-trifluroethane (TFE) was used in experiments to determine the population distribution of excited molecules produced by infrared multiphoton absorption induced by high power TEA CO2 lasers operating at 1079.85 cm−1 [9.6 μm R(22) line]. Optoacoustic measurements of absorbed laser power provided a measure of the mean energy of the population distribution, while very low pressure photolysis measurements of the collision-free decomposition yield gave information about the high-energy tail of the distribution. The experimental results were accurately simulated using a Master Equation model that incorporated Quack's statistical–dynamical theory of infrared multiphoton absorption (cases B and C), RRKM unimolecular reactions (three channels), and collisional energy transfer. The computer simulations included known TFE molecular properties and only four adjustable parameters, which were very highly constrained in order to fit the experimental data. From the simulations, we conclude that the optical coupling matrix elements are dramatically reduced in magnitude for energies above the reaction thresholds. This effect is symptomatic of the vibrational anharmonicity due to the presence of the reaction channels, even in molecules that have not yet reacted, resulting in vibrational frequency shifts of the absorption lines out of resonance with the laser line. This effect is expected to be present and observable in other highly vibrationally excited molecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449574
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  • 6
    Electronic Resource
    Electronic Resource
    Vibrationally excited populations from IR-multiphoton absorption. II. Infrared fluorescence measurements (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 6261-6267 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Infrared emission spectra were obtained for 1, 1, 2-trifluorethane (TFE) excited by infrared multiphoton absorption (1079.85 cm−1). The emission features show that the HF reaction product is formed in vibrational states up to about v=3. Furthermore, emission attributed to F–C≡C–H was observed near 3320 cm−1, indicating that the difluoroethylene primary products of TFE decomposition undergo secondary photolysis; since the difluoroethylene products at room temperature do not absorb laser light, they must be formed vibrationally excited. The emission from the C–H stretch modes of TFE was readily identified near 2980 cm−1 and the emission intensity was obtained as a function of laser fluence. These data are in excellent agreement with predictions based on the theoretical expression for fluorescence intensity and the reconstructed populations determined by the Master Equation calculations described in the preceding paper. These results provide additional support for the accuracy of the reconstructed population distributions and for the theory relating infrared fluorescence intensity to total vibrational energy in polyatomic molecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449575
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  • 7
    Electronic Resource
    Electronic Resource
    Collisional energy transfer and macroscopic disequilibrium. Application to azulene (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 124-132 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The theory of macroscopic observables, which allows a model-independent analysis of collisional relaxation, is applied to selected high-quality experimental data on infrared fluorescence (IRF) from collisional deactivation of azulene excited to ∼30 000 cm−1 by single-photon absorption from a 337 nm laser. Particular attention is paid to obtaining a secure relation between the experimental IRF intensity signal and the azulene bulk-average vibrational energy 〈〈y〉〉. The azulene system turns out to be special in two respects: the initial population distribution immediately following the laser shot can be reasonably approximated by a delta function distribution, and the time decay of 〈〈y〉〉 is a simple exponential over almost half the energy range. Under these conditions, it can be shown that the initial value of the macroscopic bulk-average energy transfer observable 〈〈ΔE〉〉 is identical to the microscopic per collision average 〈ΔE〉, which, in the azulene case, obeys the linear sum rule, i.e., is linearly dependent on excitation energy. These conclusions, which are free of assumptions concerning the nature of the transition probability, as well as the actual numerical values obtained, are in substantial agreement with the results of an earlier analysis of the data, which used a different approach based on the same microcanonical relationship connecting fluorescence intensity and vibrational energy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449804
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  • 8
    Electronic Resource
    Electronic Resource
    Vibrational energy transfer in shock-heated norbornene (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 4953-4966 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Recently, Kiefer et al. [J. H. Kiefer, S. S. Kumaran, and S. Sundaram, J. Chem. Phys. 99, 3531 (1993)] studied shock-heated norbornene (NB) in krypton bath gas using the laser-schlieren technique and observed vibrational relaxation, unimolecular dissociation (to 1,3-cyclopentadiene and ethylene), and dissociation incubation times. Other workers have obtained an extensive body of high-pressure limit unimolecular reaction rate data at lower temperatures using conventional static and flow reactors. In the present work, we have developed a vibrational energy transfer-unimolecular reaction model based on steady-state RRKM calculations and time-dependent master equation calculations to satisfactorily describe all of the NB data (incubation times, vibrational relaxation times, and unimolecular rate coefficients). The results cover the temperature range from ∼300 to 1500 K and the excitation energy range from ∼1 000 to 18 000 cm−1. Three different models (based on the exponential step-size distribution) for the average downward energy transferred per collision, 〈ΔE〉down were investigated. The experimental data are too limited to enable the identification of a preferred model and it was not possible to determine whether the average 〈ΔE〉down is temperature dependent. However, all three 〈ΔE〉down models depend linearly on vibrational energy and it is concluded that standard unimolecular reaction rate codes must be revised to include energy-dependent microcanonical energy transfer parameters. The choice of energy transfer model affects the deduced reaction critical energy by more than 2 kcal mol−1, however, which shows the importance of energy transfer in determining thermochemistry from unimolecular reaction fall-off data. It is shown that a single set of Arrhenius parameters gives a good fit of all the low temperature data and the shock-tube data extrapolated to the high pressure limit, obviating the need to invoke a change in reaction mechanism from concerted to diradical for high temperature conditions. Some possible future experiments are suggested. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470581
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  • 9
    Electronic Resource
    Electronic Resource
    Absolute integrated cross sections for some O2 Herzberg I transitions near 248–249 nm (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 6-13 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A frequency doubled tunable dye laser system with ∼0.4 cm−1 resolution was used to measure the integrated absorption cross sections of more than 20 rotational transitions in the O2 Herzberg I (A 3Σ+u←X 3Σ−g) 8-0 and 9-0 vibrational bands near 248 nm and 249 nm. Oxygen pressures from 200 to 800 Torr and path lengths from 5 to 25 m were employed. The measured absorbances were fitted using a nonlinear least squares analysis and Beer's Law to obtain absolute values for the individual transition integrated cross sections in good agreement with a recent spectral simulation and experimental data. By using the spectral simulation in conjunction with the present experimental results, total oscillator strengths in reasonable agreement with literature values were estimated for the 8-0 and 9-0 vibrational bands. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469624
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  • 10
    Electronic Resource
    Electronic Resource
    Excitation of CO2 by energy transfer from highly vibrationally excited benzene derivatives (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 8108-8119 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The time-resolved infrared fluorescence technique has been used to study V–V and V–T/R energy transfer to carbon dioxide from highly excited benzene, benzene-d6, toluene, and toluene-d8. The highly vibrationally excited aromatics in the electronic ground state are obtained by radiationless transitions after pumping with a KrF laser at 248 nm to the S1 excited electronic level. The V–V energy transfer from the excited parent to the asymmetric stretch mode of CO2 was measured by observing the characteristic emission of CO@B|2 near 4.3 μm. From these measurements, the probability per collision of formation of CO*2 was determined as a function of the internal energy in the excited aromatic. In all cases investigated, this probability is ≤0.1% at the initial excitation energy of 40 000 cm−1 and it is approximately directly proportional to the vibrational energy of the excited aromatic. The total concentration of CO@B|2 produced as a result of the many collisions needed to totally deactivate the excited aromatic amounted to 〉5% of the initial concentration of the excited aromatic and the quantitative values obtained are in excellent agreement with other work.A simple dipole–dipole interaction model is shown to explain the observed magnitude of V–V energy transfer and it is used to predict the amount of energy transferred to the bending mode of CO2. A key feature of this model is that the states of the highly vibrationally excited polyatomic are assumed to be broadened by rapid intramolecular vibrational redistribution of energy. In addition to the V–V energy-transfer measurements, the average energy lost per collision by the excited aromatic was determined as a function of the vibrational energy of the aromatic, and the rate constants were determined for CO*2 deactivation by the nondeuterated species. For the deuterated species, the results implicated a contribution from resonant V–V transfer between the C–D stretch modes and the asymmetric stretch mode of CO2. The overall results for the CO2 collider gas indicate that V–V energy transfer contributes a relatively small portion of the total energy transfer, and that portion can be described with the dipole–dipole interactions model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461290
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