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  • 1
    Electronic Resource
    Electronic Resource
    Vibrational energy transfer in OH A 2Σ+ between 195 and 295 K (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 9427-9432 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Vibrational energy transfer (VET) v′=1→0 and electronic quenching of v′=1 and 0 in the A 2Σ+ electronically excited state of the OH radical has been studied over the temperature range 195 to 295 K. The colliders investigated were N2, O2, and CO2. Laser-induced fluorescence experiments were conducted in a flow cell with photolytic production of OH; both fluorescence intensity and time decay measurements were made. The VET cross sections are found to increase with decreasing temperature, suggestive of attractive force interactions in the VET process. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481562
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  • 2
    Electronic Resource
    Electronic Resource
    Transition probabilities in OH A 2Σ+−X 2Πi: Bands with v′=2 and 3 (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 6262-6267 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Experimental relative vibrational band emission coefficients have been measured in the A 2Σ+−X 2Πi electronic system of the OH radical. Branching ratios for the sequences v′=2, v″=0–5 and v′=3, v″=0–6 were determined using laser-induced fluorescence in a low pressure methane–oxygen flame. We accounted for potential error contributed by rotational and vibrational energy transfer and fluorescence polarization. These transition probabilities complete a set of experimental data, which are used in a separate study to determine the optimum electronic transition moment of the OH A-X system. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473644
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  • 3
    Electronic Resource
    Electronic Resource
    Transition probabilities and electronic transition moments of the A 2Σ+–X 2Π and D 2Σ+–X 2Π systems of nitric oxide (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 7405-7415 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Dispersed fluorescence scans of the A–X(4,v″) and D–X(0,v″) progressions of nitric oxide, after two-photon excitation, are used to determine the electronic transition moments of these band systems. The measured collision free lifetimes of 206±7 ns for A 2Σ+, v′=0, and 18±1 ns for D 2Σ+, v′=0 are used to place transition probabilities on an absolute basis. The branching ratio for D→X is 3.0±0.3 times that for D→A and more than 30 times that for D→C. The ratio of two-photon absorption cross sections for D–X(0,0)/A–X(4,0) is 6±2 and the photoionization probability from D, v′=0 is larger than from A, v′=4 at 375 nm. Also, the two-photon excitation of A–X(4,0) has an unusual intensity distribution, probably due either to interference between intermediate states in the excitation or to anomalies in the photoionization step. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480064
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  • 4
    Electronic Resource
    Electronic Resource
    Transition probabilities in the A 2Σ+−X 2Πi electronic system of OH (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 439-448 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A complete set of experimental vibrational band transition probabilities, including recent measurements on v′=2 and 3, allows us to calculate an empirical electronic transition moment, Re(r), for the A 2Σ+−X 2Πi system of OH, over the range of internuclear distance 0.70–1.70 Å. A comparison with an ab initio moment confirms that theoretical shape and validates its quantitative results, as the calculated Re(r) is within experimental uncertainty of the present result. The experimentally derived Re(r) is used along with Rydberg–Klein–Rees (RKR) wave functions to calculate transition probabilities for a wide range of vibrational and rotational levels. The study is extended to the isotope OD. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476582
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  • 5
    Electronic Resource
    Electronic Resource
    Radiative and predissociative rates for NO A 2Σ+v′=0–5 and D 2Σ+v′=0–3 (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 9411-9416 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Two-photon laser-induced fluorescence of the NO A–X(0–5,0) and D–X(0–3,0) bands is used to obtain collision-free lifetimes of the A v′=0–5 and D v′=0–3 levels in a flow cell. The vibrational trend from NO A v′=0 to v′=3 is small, with radiative lifetimes between 205±7 to 184±8 ns, respectively, in agreement with recent calculations derived from branching ratio measurements and ab initio calculations. Rotationally resolved measurements in the NO A 2Σ+ and D 2Σ+ states reveal very different lifetime behavior for these nearly isoenergetic levels above the NO X 2Π state dissociation limit. The rotational lifetimes of A 2Σ+v′=4,5 and D 2Σ+v′=0 are basically constant with rotation. However, D 2Σ+v′=1, 2, and 3 have a strong rotational dependence, decreasing nearly threefold between N′=0 and 20. These observations suggest weak coupling with the ground-state continuum to be the most likely predissociation mechanism for the high A 2Σ+ levels, and rotational on heterogeneous (gyroscopic) predissociation by the C 2Π is the dominant mechanism for the D 2Σ+ state above v′=0. The collision-free lifetime of E 2Σ+v′=0 is 40±3 ns, and that for F 2Δv′=0 is 27±3 ns. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481560
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  • 6
    Electronic Resource
    Electronic Resource
    Electronic transition moment and rotational transition probabilities in CH. I. A 2Δ–X 2Π system (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 2146-2155 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Vibrational band transition probabilities of the A–X electronic system of CH, v′=0, 1, and 2, have been measured in a low pressure flame using laser-induced fluorescence. These results improve earlier experiments that were complicated by energy transfer contributions, and expand measurements to very weak off-diagonal bands such as 0,2 and 1,3. The electronic transition moment derived from the vibrational branching ratio measurements differs slightly from ab initio calculations. Hönl–London factors using a mixed coupling scheme have been tested by experiment. Finally, a combination of these results with previously measured radiative lifetimes yields absolute absorption and emission coefficients for this system. A comparison between computed radiative lifetimes and collision-free experimental lifetimes suggests a predissociation rate in v′=0, N′(approximately-greater-than)17 of ∼1.5×105 s−1. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470970
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  • 7
    Electronic Resource
    Electronic Resource
    Vibrationally excited O2 in flames: Measurements on v‘=9–11 by laser-induced fluorescence (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 2500-2504 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Vibrationally-excited ground state O2 is detected in a CH4/O2 flame in levels v‘=9–11 by laser-induced fluorescence in the B 3Σ−u–X 3Σ−g Schumann–Runge system. Accurate line positions are measured by calibration against OH(A–X) lines appearing in the same spectra. Signal levels indicate that measurements up to at least v‘=18 should be practical in such flames. The absolute energies of the three vibrational levels agree very well with RKR calculations of Albritton, based on earlier experimental work, but there is substantial disagreement for v‘=11 with the extensive data of Creek and Nicholls.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452101
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  • 8
    Electronic Resource
    Electronic Resource
    Quenching of OH(A 2Σ+, v'=0) by NH3 from 250 to 1400 K (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 1898-1903 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The rate constant for collisional removal of the v′=0 level of the A 2Σ+ excited state of the OH radical by NH3 is measured over the temperature range 250–1400 K. The thermally averaged cross section σQ near room temperature is roughly twice its value at 900 K of ∼40 A(ring)2. Between 850 and 1400 K, no variation of σQ with temperature is observed. This temperature dependence is consistent with a quenching mechanism dominated by long range attractive forces.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451133
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  • 9
    Electronic Resource
    Electronic Resource
    NH A 3Πi quenching at 1400 K (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 4970-4975 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have measured electronic quenching rate constants, kQ, in the NH A 3Πi, v'=0 state for several quencher molecules at 1400 K. The NH radicals were produced in a laser pyrolysis apparatus when a mixture of SF6, CF4, NH3, and added quencher was irradiated by a CO2 laser. The ground state NH radicals were then excited to the A state by a pulsed tunable dye laser. The fluorescence decay rates as a function of added quencher pressure yielded the rate constants. The thermally averaged cross sections, σQ=kQ/〈v〉, for NH at 1400 K are all smaller than those observed for OH at 1200 K in this laboratory. In most cases, our high temperature σQ's are the same as those observed elsewhere at room temperature. These experimental σQ's are all less than those calculated with an attractive forces "collision complex'' model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449983
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  • 10
    Electronic Resource
    Electronic Resource
    Radiative lifetime and quenching of the 3p 4D0 state of atomic nitrogen (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 4876-4884 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The radiative lifetime of nitrogen atoms in the 3p 4D0 state is determined to be 43±3 ns, and the total removal rate constants from the excited 3p 4D0 state of nitrogen atoms are measured for collisions with He, Ne, Ar, Kr, Xe, and N2. In a low pressure discharge flow reactor, the 3p 4D0 state is prepared by two-photon excitation from the 4S0 ground state of atomic nitrogen. Time-resolved fluorescence from the 3p 4D0→3s 4P transition monitors the temporal evolution of the population in the 3p 4D0 state. As the rare gases become heavier with a more complex electron cloud, the quenching rate constants increase from less than 0.6×10−11 cm3 s−1 for He to a value of 66±12×10−11 cm3 s−1 for Xe. Collision mechanisms which might account for such a dramatic increase are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452658
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