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  • 1
    Electronic Resource
    Electronic Resource
    Laser-induced fluorescence in the B˜–X˜ system of the HCO radical (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 7601-7608 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The spectroscopy of the B˜ 2A'–X˜ 2A' system of the formyl radical has been studied by laser-induced fluorescence. HCO was generated by photolysis of acetaldehyde, and a tunable laser operated near 245 nm excited eight bands of B˜–X˜. The (0,0,2)–(0,0,0) band has been rotationally analyzed, yielding A'=14.46 cm−1 and (B'+C')/2=1.13 cm−1 for this slightly asymmetric top; asymmetry splitting and spin doubling are observed. The intense branches have ΔK=0 but there also are weaker perpendicular components with the transition moment near the b axis. Vibronic transition energies agree with those from matrix absorption but with a 130 cm−1 blueshift. Resolved fluorescence spectra to X˜ levels as high as 15 000 cm−1 furnish vibrational constants for the ground state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459391
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  • 2
    Electronic Resource
    Electronic Resource
    Quenching and vibrational energy transfer in the B 2Π state of the NS molecule (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 5343-5351 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Quenching and vibrational energy transfer in the B2Π state of the NS free radical have been studied using temporally and spectrally resolved laser-induced fluorescence in a low-pressure discharge flow reactor. The collision partners were He, Ar, H2, N2, O2, SF6, CO2, and N2O. Total removal cross sections show an oscillatory behavior with v' in the range of unperturbed levels, v'=4–7, for all colliders studied save O2 where a nearly monotonic increase is seen. Vibrational transfer occurs for H2 and the polyatomics; the rates vary little with v'. Δv=2 transfer occurs with the polyatomic colliders for v'=5. Fluorescence decay traces from the perturbed v'=3 and 8 levels differ from the unperturbed levels and from each other. v'=3 is perturbed by quartets and shows "gateway'' level behavior whereas v'=8 is perturbed by a doublet and shows efficient interelectronic transfer for all rotational levels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457665
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  • 3
    Electronic Resource
    Electronic Resource
    Electronic quenching, fluorescence lifetime, and spectroscopy of the A 3Πu state of NCN (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 1987-1993 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Laser-induced fluorescence of the NCN radical was observed downstream of a microwave discharge of N2 and CF4 in He via the A 3Πu–X 3Σ−g transition near 329 nm. The zero-pressure fluorescence lifetime of the 000 vibrational level of the A state was measured from the time-resolved laser-induced fluorescence to be 183±6 ns. Other spectral features were observed both to the blue and red of the 000–000 band. The blue-shifted features are tentatively assigned to the 020–000, 100–000, 030–010, and 110–010 vibrational bands. Quenching cross sections were determined for NCN (A 3Πu, 000) at 300 K for Ar, Kr, Xe, O2, CO, CO2, N2O, SF6, NO, and NO2. The molecules He, N2, and CF4 are inefficient quenchers and upper limits only were obtained. The large variation in cross section among the colliders does not correlate with predictions of simple electronic quenching models.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457057
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  • 4
    Electronic Resource
    Electronic Resource
    Rotational level dependent quenching of the A 3Πi, v'=0 state of NH (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 3566-3573 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Quenching cross sections σQ have been measured for several rotational levels N' in the A 3∏i, v'=0 state of NH, for a variety of collision partners. Ground state NH was generated in a room temperature discharge flow and excited with a pulsed laser, and the time decay of fluorescence was measured. The radiative lifetime for the levels N'=1 to 5 is 418 ± 8 ns. The σQ's are generally large, up to 90 A(ring)2, and decrease with increasing N'. This indicates the influence of an anisotropic, attractive interaction in most but not all cases. The present values of σQ are compared with those of other experiments; because σQ depends both on N' and collision energy, experimental conditions must be carefully specified to yield results which are readily comparable.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455815
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  • 5
    Electronic Resource
    Electronic Resource
    Vibrational relaxation of OH (X 2Πi, v=2) (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 2174-2181 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Vibrational relaxation rates for the v=2 level of the X 2Πi state of the OH radical have been measured in a low pressure flow system, using a novel two-laser pump-and-probe technique. The OH is prepared in the v=2 level by overtone pumping (2←0) and monitored by ultraviolet laser-induced fluorescence in the (1,2) band of the A–X system. Scanning the time delay between the lasers at a given collider pressure produces exponential decay whose rate as a function of collider pressure yields the rate constant. We determine values (all cm3 s−1 units) for NH3: (1.20±0.15)×10−10; CH4: (2.3±0.2)×10−12; CO2: (6.7±1.1)×10−13; N2O: (4.6±0.6)×10−13; O2: (2.6±0.54)×10−13; N2 and H2: ≤10−14. Except for ammonia, these are two to three orders of magnitude smaller than those measured for relaxation of v=1 in the A 2Σ+ excited state of OH, where attractive forces appear to play a role.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456671
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  • 6
    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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  • 7
    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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  • 8
    Electronic Resource
    Electronic Resource
    Temperature dependent quenching of the A 2Σ+ and B 2Π states of NO (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 5211-5217 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Collisional quenching of the v'=0 vibrational levels of the A 2Σ+ and B 2Π states of nitric oxide has been studied over the temperature range 300 to 750 K. The pressure dependence of the time decay of laser-induced fluorescence, in a slowly flowing heated cell, furnished the quenching cross sections σQ. NO and O2 quench the A state rapidly but with no temperature dependence; σQ=37 and 21 A(ring)2, respectively. σQA for H2O drops from 105 A(ring)2 at 300 K to 34 A(ring)2 at 750 K. σQB for O2 is independent of temperature but σQB for NO drops twofold and for H2O decreases by a factor of 3 over the temperature range studied. This variation among these colliders cannot be explained by a uniform, simple picture of the collision dynamics. Evidence is seen for B→A transfer proceeding through an intermediate state, perhaps a 4Π.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458604
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  • 9
    Electronic Resource
    Electronic Resource
    Intramultiplet energy transfer in the collisions of 3p 4D0 nitrogen atoms with nitrogen molecules (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 2200-2205 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Two-photon excitation at 211 nm combined with wavelength-resolved detection near 870 nm is used to study intramultiplet energy transfer in the 2s22p23p 4D0 state of nitrogen atoms resulting from collisions with nitrogen molecules. The thermally averaged cross sections at 300 K vary from 36±10 A(ring)2 for 4D01/2→4D03/2 to 3±3 A(ring)2 for 4D07/2→4D01/2. The cross sections for ΔJ=1 are larger than for ΔJ=2 which in turn are larger than for ΔJ=3. When 3p4D07/2 is excited with linearly polarized light, the fluorescence polarization is nonzero and independent of N2 pressure. Thus, the cross section for transfer between magnetic sublevels is smaller than those for transfer out of that fine-structure level.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457029
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  • 10
    Electronic Resource
    Electronic Resource
    Rotational level dependence of the electronic quenching of NH2A˜ by helium (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 237-241 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The rotational level dependence of the electronic quenching of the A˜2A1 state of the NH2 radical is investigated by time-resolved laser-induced fluorescence. Quenching of ∑(0,9,0) is found to increase monotonically with rotational level from 2×10−11 cm3s−1 for N'=0 to 7×10−11 cm3 s−1 for N'=7. Measurements on the neighboring ∑(0,7,0), Π(0,8,0), and Π(0,10,0) vibronic levels show no significant rotational level dependence. The behavior in ∑(0,9,0) cannot be satisfactorily explained by either molecular collision dynamics or by state mixing.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459597
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