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  • 1990-1994  (42)
  • 1
    Electronic Resource
    Electronic Resource
    The production of O(3P) in the 157 nm photodissociation of CO2 (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 2897-2901 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The branching ratio was measured for the production of O(3P) in the photodissociation of CO2 at 157 nm. A gas mixture consisting of CO2, H2, and Ar was irradiated with an F2 excimer laser, while the relative concentration of O(3P) was monitored continuously using atomic resonance fluorescence. The O(1D) product was removed by either reacting with H2 or by being quenched by CO2. At a high H2/CO2 ratio a residual O(3P) signal persisted which was due to the nascent photofragments of CO2. A Stern–Volmer analysis indicated that the fraction of O(3P) produced is 5.9%. Control experiments using O2 and N2O as precursor molecules confirmed this interpretation of the data. A mechanism is proposed based on curve crossing from the 1B2 to the 3B2 potential energy surfaces of CO2. Since the 1B2 state is bent, a substantial fraction of the absorbed energy is initially in bending motion, resulting in a long-lived chaotic trajectory which has many opportunities to cross over to the triplet surface. A similar model proposed by Tully to explain the quenching of O(1D) by CO is in qualitative agreement with our data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457937
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  • 2
    Electronic Resource
    Electronic Resource
    The intramolecular kinetic isotope effect for the reaction O(3P)+HD (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 7382-7393 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The branching ratio for the reaction O(3P)+HD to produce OH and OD was measured over the temperature range 339–500 K using a discharge-flow reactor. The OH and OD products were detected using laser-induced fluorescence under steady-state conditions. In order to determine the relative concentrations of OH and OD produced in this reaction, calibration runs were performed using the reactions of O(3P)+H2 and D2 to produce known relative amounts of the same species. Kinetic modeling showed that secondary reactions and the production of vibrationally excited OD did not affect the measured branching ratio. We found that the OH/OD ratio increased rapidly with decreasing temperature, in qualitative agreement with theory, showing that the reaction is dominated by tunneling below 400 K. At the lowest temperatures, the observed branching ratio is larger than predicted. The reason for this discrepancy is not known.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458224
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  • 3
    Electronic Resource
    Electronic Resource
    The origin of small and large molecule behavior in the vibrational relaxation of highly excited molecules (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 4632-4634 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An explanation is proposed for the qualitatively different types of behavior that have been reported for the vibrational relaxation of highly excited diatomic and polyatomic molecules. It is argued that all of the diatomic molecules that have been studied in bulk relax adiabatically at room temperature. In contrast, large polyatomic molecules have low frequency modes which act at "doorway'' modes for the rest of the molecules, producing an impulsive relaxation mechanism. The theoretical work of Nesbitt and Hynes showed that impulsive collisions result in an exponential decay of the average vibrational energy of a Morse oscillator, whereas adiabatic collisions produce nonexponential power law behavior. We propose that this result explains a large body of data for the vibrational relaxation of small and large molecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457729
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  • 4
    Electronic Resource
    Electronic Resource
    Coherent laser control of the resonance-enhanced multiphoton ionization of HCl (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 8622-8624 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Coherent control of the ionization of HCl was achieved by simulataneous 3+1 and 1+1 multiphoton excitation in a molecular beam machine, using either three 336 nm photons or one 112 nm photon to resonantly excite the intermediate j 3Σ−(Ω=0+) state. The phase difference between the two laser beams was continuously varied by passing the radiation through a cell containing either Ar or H2 gas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460047
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  • 5
    Electronic Resource
    Electronic Resource
    The multiphoton ionization spectrum of HBr. I. 74 000 to 85 000 cm−1 (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 4624-4636 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The technique of resonantly enhanced multiphoton ionization with time-of-flight mass resolution has been used to measure the two-photon absorption spectrum of HBr. We have analyzed 37 bands and assigned them to transitions to the valence, ion-pair state and to Rydberg states belonging to the sσ, pσ, dσ, pπ, dπ, and dδ manifolds. Our results are in excellent agreement with the earlier work of Ginter, Ginter, and Tilford. In addition, we have analyzed twelve new electronic states as well as numerous bands of vibrationally excited levels of previously known electronic states. Strong mixing was observed among the 0+ states.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458702
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  • 6
    Electronic Resource
    Electronic Resource
    The multiplet state distribution of O(3PJ) produced in the 193 nm photodissociation of SO2 (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 868-869 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The multiplet state distribution of oxygen atoms produced in the photodissociation of SO2 was measured in a pump-and-probe experiment. An ArF laser was used to dissociate the parent molecule, while the O(3P) product was detected by two-photon laser-induced fluorescence under collisionless conditions. The multiplet populations were found to be 59.2%±5.0%, 29.5%±3.2%, and 11.4%±3.3% for J=2, 1, and 0, respectively. These results are indistinguishable from the statistical distribution of 5:3:1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459462
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  • 7
    Electronic Resource
    Electronic Resource
    Vibrational relaxation of highly excited SiF4 and C6F5H by Ar (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 6011-6016 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The vibrational relaxation of SiF4 and C6F5H in an Ar bath was measured as a function of initial energy using the method of time-resolved optoacoustics. SiF4 was found to relax nonexponentially, with a rate constant which varied approximately as the vibrational energy raised to the 3/2 power. This behavior is similar to that observed earlier for SF6+Ar below the bottleneck. In contrast, C6F5H was observed to decay exponentially, as expected for a large molecule in the quasicontinuum. These two types of behavior are discussed in the context of previously proposed propensity rules for the vibrational relaxation of highly excited molecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458372
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  • 8
    Electronic Resource
    Electronic Resource
    Pulmonary Hemorrhage Induced by Intratracheal Administration of Human Leukocyte Elastase in Hamsters (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 624 (1991), S. 0 
    Details
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1749-6632.1991.tb17037.x
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  • 9
    Electronic Resource
    Electronic Resource
    Perturbations in the multiphoton ionization spectrum of the F 1Δ state of HCl (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 854-864 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The 2+1 REMPI spectra of the F(0–0), F(1–0), E(0–0), and V(11–0) transitions of HCl were measured in a time-of-flight molecular beam machine. Both room temperature HCl, and rotationally and vibrationally excited HCl obtained by photodissociating vinyl chloride at 193 nm, were used. Several anomalies in the F state were observed. These include a decrease in intensity of the P, Q, and R branches between J'=3 and J'=10 for the 0–0 transition, a falloff in intensity for J'〉5 for the P, Q, and R branches of the 1–0 transition, and an enhanced intensity loss of the Q(9) line of the 0–0 transition. Accurate values of the lambda-doublet splitting constants for these transitions were also obtained. The intensity loss in the 0–0 transition is due to an interaction with some unobserved bound state, which could also explain the 1–0 perturbation. A candidate for the perturbing state is the e 3Σ+(1). The isolated perturbation of the Q(9), 0–0 line could be caused by an interaction with the g(0+) state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461093
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  • 10
    Electronic Resource
    Electronic Resource
    Doppler profiles and fine-structure branching ratios of O(3Pj) from photodissociation of carbon dioxide at 157 nm (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 7311-7316 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The O(2p 3Pj) (j=2, 1, and 0) fragments produced in the 157 nm photodissociation of CO2 were detected by resonance-enhanced multiphoton ionization in a molecular beam. The Doppler profiles and fine-structure branching ratios were measured for the oxygen-atom photofragment in the 3Pj states. The Doppler profiles were analyzed to give an anisotropy parameter of β=2.0±0.2 and an internal energy equivalent to 3.9±0.3 vibrational quanta of CO. The fine-structure populations were found to be 0.70±0.05, 0.16±0.03, and 0.14±0.03 (with error bars of ±σ) for j=2, 1, and 0, respectively. A mechanism is proposed in which complex on the 1B2 surface undergoes intersystem crossing to the 3B2 surface. A phase-space model with a constraint on the impact parameter is shown to be consistent with the observed energy release. The nonstatistical fine-structure population could be caused by long-range interactions on the triplet surface. In a bulb experiment, O(3P) was produced by quenching of O(1D). The fine-structure populations of the resulting O(3Pj) were 0.64±0.04, 0.25±0.04, and 0.11±0.04. This state distribution is consistent with a long-lived complex which decays to give statistical products.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461408
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