Abstract

This paper describes photochemical effects observed during two-photon 1S–2S excitation of atomic hydrogen in flames using 243-nm laser radiation. An I 4 intensity dependence is observed in regions of the flame where the natural atomic concentration is low, suggesting an I 2 photochemical production mechanism, which we believe is due to two-photon excitation of water molecules, which then predissociate to form H and OH fragments. In a measurement of OH created in the flame by the 243-nm beam, we observe the same I 2 intensity dependence with the laser detuned from the atomic hydrogen 1S–2S resonance, but an apparent I 3,4 dependence is observed when the laser is tuned to the resonance. We believe that a second photochemical mechanism contributes at the resonance, namely, two-photon excitation of H, followed by collisional energy transfer to water molecules, which then fall apart into H and OH fragments. We model this process and show that a combination of I 2 and I 4 dependences can lead to an intensity dependence that mimics a single I 3,4 dependence over a limited range of intensities.

© 1989 Optical Society of America

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References

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  1. J. E. M. Goldsmith, “Multiphoton Excitation Techniques for Combustion Diagnostics,” AIP Conf. Proc. 146, 279 (1986), and references therein.
    [CrossRef]
  2. A. W. Miziolek, M. A. DeWilde, “Multiphoton Photochemical and Collisional Effects During Oxygen-Atom Flame Detection,” Opt. Lett. 9, 390 (1984).
    [CrossRef] [PubMed]
  3. J. E. M. Goldsmith, “Photochemical Effects in Two-Photon-Excited Fluorescence Detection of Atomic Oxygen in Flames,” Appl. Opt. 26, 3566 (1987).
    [CrossRef] [PubMed]
  4. J. E. M. Goldsmith, “Photochemical Effects in 205-nm, Two-Photon-Excited Fluorescence Detection of Atomic Hydrogen in Flames,” Opt. Lett. 11, 416 (1986).
    [CrossRef] [PubMed]
  5. J. E. M. Goldsmith, “Flame Studies of Atomic Hydrogen and Oxygen Using Resonant Multiphoton Optogalvanic Spectroscopy,” in Twentieth Symposium (International) on Combustion (Combustion Institute, Pittsburgh, PA, 1984), pp. 1331–1337.
  6. J. E. M. Goldsmith, “Two-Step Saturated Fluorescence Detection of Atomic Hydrogen in Flames,” Opt. Lett. 10, 116 (1985).
    [CrossRef] [PubMed]
  7. This burner was purchased from McKenna Products, Pittsburg, CA 94565.
  8. C. Fotakis, C. B. McKendrick, R. J. Donovan, “Two-Photon Excitation of H2O and D2O with a KrF Laser (248 nm): Photofragment Fluorescence from OH and OD (A2Σ+)”, Chem. Phys. Lett. 80, 598 (1981).
    [CrossRef]
  9. A. Hodgson, J. P. Simons, M. N. R. Ashfold, J. M. Bayley, R.N. Dixon, “Quantum-State-Selected Photodissociation of H2O (C‾1B1),” Chem. Phys. Lett. 107, 1 (1984).
    [CrossRef]
  10. G. Meijer, J. J. ter Meulen, P. Andresen, A. Bath, “Sensitive Quantum State Selective Detection of H2O and D2O by (2+1)-Resonance Enhanced Multiphoton Ionization,” J. Chem. Phys. 85, 6914 (1986).
    [CrossRef]
  11. I. Tanaka, T. Carrington, H. P. Broida, “Photon-Dissociation of Water: Initial Nonequilibrium Populations of Rotational States of OH(2Σ+),” J. Chem. Phys. 35, 750 (1961);T. Carrington, “Angular Momentum Distribution and Emission Spectrum of OH (2Σ+) in the Photodissociation of H2O,” J. Chem. Phys. 41, 2012 (1964).
    [CrossRef]
  12. J. E. M. Goldsmith, “Multiphoton-Excited Fluorescence Measurements of Atomic Hydrogen in Low-Pressure Flames,” in Twenty-Second Symposium (International) on Combustion (Combustion Institute, Pittsburgh, PA, 1988), in press.
  13. S. J. Harris, A. M. Weiner, R. J. Blint, J. E. M. Goldsmith, “Concentration Profiles in Rich and Sooting Ethylene Flames,” in Twenty-First Symposium (International) on Combustion (Combustion Institute, Pittsburgh, PA, 1986), pp. 1033–1045.

1987 (1)

1986 (3)

J. E. M. Goldsmith, “Photochemical Effects in 205-nm, Two-Photon-Excited Fluorescence Detection of Atomic Hydrogen in Flames,” Opt. Lett. 11, 416 (1986).
[CrossRef] [PubMed]

J. E. M. Goldsmith, “Multiphoton Excitation Techniques for Combustion Diagnostics,” AIP Conf. Proc. 146, 279 (1986), and references therein.
[CrossRef]

G. Meijer, J. J. ter Meulen, P. Andresen, A. Bath, “Sensitive Quantum State Selective Detection of H2O and D2O by (2+1)-Resonance Enhanced Multiphoton Ionization,” J. Chem. Phys. 85, 6914 (1986).
[CrossRef]

1985 (1)

1984 (2)

A. W. Miziolek, M. A. DeWilde, “Multiphoton Photochemical and Collisional Effects During Oxygen-Atom Flame Detection,” Opt. Lett. 9, 390 (1984).
[CrossRef] [PubMed]

A. Hodgson, J. P. Simons, M. N. R. Ashfold, J. M. Bayley, R.N. Dixon, “Quantum-State-Selected Photodissociation of H2O (C‾1B1),” Chem. Phys. Lett. 107, 1 (1984).
[CrossRef]

1981 (1)

C. Fotakis, C. B. McKendrick, R. J. Donovan, “Two-Photon Excitation of H2O and D2O with a KrF Laser (248 nm): Photofragment Fluorescence from OH and OD (A2Σ+)”, Chem. Phys. Lett. 80, 598 (1981).
[CrossRef]

1961 (1)

I. Tanaka, T. Carrington, H. P. Broida, “Photon-Dissociation of Water: Initial Nonequilibrium Populations of Rotational States of OH(2Σ+),” J. Chem. Phys. 35, 750 (1961);T. Carrington, “Angular Momentum Distribution and Emission Spectrum of OH (2Σ+) in the Photodissociation of H2O,” J. Chem. Phys. 41, 2012 (1964).
[CrossRef]

Andresen, P.

G. Meijer, J. J. ter Meulen, P. Andresen, A. Bath, “Sensitive Quantum State Selective Detection of H2O and D2O by (2+1)-Resonance Enhanced Multiphoton Ionization,” J. Chem. Phys. 85, 6914 (1986).
[CrossRef]

Ashfold, M. N. R.

A. Hodgson, J. P. Simons, M. N. R. Ashfold, J. M. Bayley, R.N. Dixon, “Quantum-State-Selected Photodissociation of H2O (C‾1B1),” Chem. Phys. Lett. 107, 1 (1984).
[CrossRef]

Bath, A.

G. Meijer, J. J. ter Meulen, P. Andresen, A. Bath, “Sensitive Quantum State Selective Detection of H2O and D2O by (2+1)-Resonance Enhanced Multiphoton Ionization,” J. Chem. Phys. 85, 6914 (1986).
[CrossRef]

Bayley, J. M.

A. Hodgson, J. P. Simons, M. N. R. Ashfold, J. M. Bayley, R.N. Dixon, “Quantum-State-Selected Photodissociation of H2O (C‾1B1),” Chem. Phys. Lett. 107, 1 (1984).
[CrossRef]

Blint, R. J.

S. J. Harris, A. M. Weiner, R. J. Blint, J. E. M. Goldsmith, “Concentration Profiles in Rich and Sooting Ethylene Flames,” in Twenty-First Symposium (International) on Combustion (Combustion Institute, Pittsburgh, PA, 1986), pp. 1033–1045.

Broida, H. P.

I. Tanaka, T. Carrington, H. P. Broida, “Photon-Dissociation of Water: Initial Nonequilibrium Populations of Rotational States of OH(2Σ+),” J. Chem. Phys. 35, 750 (1961);T. Carrington, “Angular Momentum Distribution and Emission Spectrum of OH (2Σ+) in the Photodissociation of H2O,” J. Chem. Phys. 41, 2012 (1964).
[CrossRef]

Carrington, T.

I. Tanaka, T. Carrington, H. P. Broida, “Photon-Dissociation of Water: Initial Nonequilibrium Populations of Rotational States of OH(2Σ+),” J. Chem. Phys. 35, 750 (1961);T. Carrington, “Angular Momentum Distribution and Emission Spectrum of OH (2Σ+) in the Photodissociation of H2O,” J. Chem. Phys. 41, 2012 (1964).
[CrossRef]

DeWilde, M. A.

Dixon, R.N.

A. Hodgson, J. P. Simons, M. N. R. Ashfold, J. M. Bayley, R.N. Dixon, “Quantum-State-Selected Photodissociation of H2O (C‾1B1),” Chem. Phys. Lett. 107, 1 (1984).
[CrossRef]

Donovan, R. J.

C. Fotakis, C. B. McKendrick, R. J. Donovan, “Two-Photon Excitation of H2O and D2O with a KrF Laser (248 nm): Photofragment Fluorescence from OH and OD (A2Σ+)”, Chem. Phys. Lett. 80, 598 (1981).
[CrossRef]

Fotakis, C.

C. Fotakis, C. B. McKendrick, R. J. Donovan, “Two-Photon Excitation of H2O and D2O with a KrF Laser (248 nm): Photofragment Fluorescence from OH and OD (A2Σ+)”, Chem. Phys. Lett. 80, 598 (1981).
[CrossRef]

Goldsmith, J. E. M.

J. E. M. Goldsmith, “Photochemical Effects in Two-Photon-Excited Fluorescence Detection of Atomic Oxygen in Flames,” Appl. Opt. 26, 3566 (1987).
[CrossRef] [PubMed]

J. E. M. Goldsmith, “Photochemical Effects in 205-nm, Two-Photon-Excited Fluorescence Detection of Atomic Hydrogen in Flames,” Opt. Lett. 11, 416 (1986).
[CrossRef] [PubMed]

J. E. M. Goldsmith, “Multiphoton Excitation Techniques for Combustion Diagnostics,” AIP Conf. Proc. 146, 279 (1986), and references therein.
[CrossRef]

J. E. M. Goldsmith, “Two-Step Saturated Fluorescence Detection of Atomic Hydrogen in Flames,” Opt. Lett. 10, 116 (1985).
[CrossRef] [PubMed]

S. J. Harris, A. M. Weiner, R. J. Blint, J. E. M. Goldsmith, “Concentration Profiles in Rich and Sooting Ethylene Flames,” in Twenty-First Symposium (International) on Combustion (Combustion Institute, Pittsburgh, PA, 1986), pp. 1033–1045.

J. E. M. Goldsmith, “Multiphoton-Excited Fluorescence Measurements of Atomic Hydrogen in Low-Pressure Flames,” in Twenty-Second Symposium (International) on Combustion (Combustion Institute, Pittsburgh, PA, 1988), in press.

J. E. M. Goldsmith, “Flame Studies of Atomic Hydrogen and Oxygen Using Resonant Multiphoton Optogalvanic Spectroscopy,” in Twentieth Symposium (International) on Combustion (Combustion Institute, Pittsburgh, PA, 1984), pp. 1331–1337.

Harris, S. J.

S. J. Harris, A. M. Weiner, R. J. Blint, J. E. M. Goldsmith, “Concentration Profiles in Rich and Sooting Ethylene Flames,” in Twenty-First Symposium (International) on Combustion (Combustion Institute, Pittsburgh, PA, 1986), pp. 1033–1045.

Hodgson, A.

A. Hodgson, J. P. Simons, M. N. R. Ashfold, J. M. Bayley, R.N. Dixon, “Quantum-State-Selected Photodissociation of H2O (C‾1B1),” Chem. Phys. Lett. 107, 1 (1984).
[CrossRef]

McKendrick, C. B.

C. Fotakis, C. B. McKendrick, R. J. Donovan, “Two-Photon Excitation of H2O and D2O with a KrF Laser (248 nm): Photofragment Fluorescence from OH and OD (A2Σ+)”, Chem. Phys. Lett. 80, 598 (1981).
[CrossRef]

Meijer, G.

G. Meijer, J. J. ter Meulen, P. Andresen, A. Bath, “Sensitive Quantum State Selective Detection of H2O and D2O by (2+1)-Resonance Enhanced Multiphoton Ionization,” J. Chem. Phys. 85, 6914 (1986).
[CrossRef]

Miziolek, A. W.

Simons, J. P.

A. Hodgson, J. P. Simons, M. N. R. Ashfold, J. M. Bayley, R.N. Dixon, “Quantum-State-Selected Photodissociation of H2O (C‾1B1),” Chem. Phys. Lett. 107, 1 (1984).
[CrossRef]

Tanaka, I.

I. Tanaka, T. Carrington, H. P. Broida, “Photon-Dissociation of Water: Initial Nonequilibrium Populations of Rotational States of OH(2Σ+),” J. Chem. Phys. 35, 750 (1961);T. Carrington, “Angular Momentum Distribution and Emission Spectrum of OH (2Σ+) in the Photodissociation of H2O,” J. Chem. Phys. 41, 2012 (1964).
[CrossRef]

ter Meulen, J. J.

G. Meijer, J. J. ter Meulen, P. Andresen, A. Bath, “Sensitive Quantum State Selective Detection of H2O and D2O by (2+1)-Resonance Enhanced Multiphoton Ionization,” J. Chem. Phys. 85, 6914 (1986).
[CrossRef]

Weiner, A. M.

S. J. Harris, A. M. Weiner, R. J. Blint, J. E. M. Goldsmith, “Concentration Profiles in Rich and Sooting Ethylene Flames,” in Twenty-First Symposium (International) on Combustion (Combustion Institute, Pittsburgh, PA, 1986), pp. 1033–1045.

AIP Conf. Proc. (1)

J. E. M. Goldsmith, “Multiphoton Excitation Techniques for Combustion Diagnostics,” AIP Conf. Proc. 146, 279 (1986), and references therein.
[CrossRef]

Appl. Opt. (1)

Chem. Phys. Lett. (2)

C. Fotakis, C. B. McKendrick, R. J. Donovan, “Two-Photon Excitation of H2O and D2O with a KrF Laser (248 nm): Photofragment Fluorescence from OH and OD (A2Σ+)”, Chem. Phys. Lett. 80, 598 (1981).
[CrossRef]

A. Hodgson, J. P. Simons, M. N. R. Ashfold, J. M. Bayley, R.N. Dixon, “Quantum-State-Selected Photodissociation of H2O (C‾1B1),” Chem. Phys. Lett. 107, 1 (1984).
[CrossRef]

J. Chem. Phys. (2)

G. Meijer, J. J. ter Meulen, P. Andresen, A. Bath, “Sensitive Quantum State Selective Detection of H2O and D2O by (2+1)-Resonance Enhanced Multiphoton Ionization,” J. Chem. Phys. 85, 6914 (1986).
[CrossRef]

I. Tanaka, T. Carrington, H. P. Broida, “Photon-Dissociation of Water: Initial Nonequilibrium Populations of Rotational States of OH(2Σ+),” J. Chem. Phys. 35, 750 (1961);T. Carrington, “Angular Momentum Distribution and Emission Spectrum of OH (2Σ+) in the Photodissociation of H2O,” J. Chem. Phys. 41, 2012 (1964).
[CrossRef]

Opt. Lett. (3)

Other (4)

This burner was purchased from McKenna Products, Pittsburg, CA 94565.

J. E. M. Goldsmith, “Flame Studies of Atomic Hydrogen and Oxygen Using Resonant Multiphoton Optogalvanic Spectroscopy,” in Twentieth Symposium (International) on Combustion (Combustion Institute, Pittsburgh, PA, 1984), pp. 1331–1337.

J. E. M. Goldsmith, “Multiphoton-Excited Fluorescence Measurements of Atomic Hydrogen in Low-Pressure Flames,” in Twenty-Second Symposium (International) on Combustion (Combustion Institute, Pittsburgh, PA, 1988), in press.

S. J. Harris, A. M. Weiner, R. J. Blint, J. E. M. Goldsmith, “Concentration Profiles in Rich and Sooting Ethylene Flames,” in Twenty-First Symposium (International) on Combustion (Combustion Institute, Pittsburgh, PA, 1986), pp. 1033–1045.

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Figures (8)

Fig. 1
Fig. 1

Apparatus used for two-step fluorescence detection of atomic hydrogen and for studies of OH produced during 243-nm irradiation of flame gases.

Fig. 2
Fig. 2

Energy levels and transitions in atomic hydrogen (not to scale) relevant to two-step fluorescence detection.

Fig. 3
Fig. 3

Atomic hydrogen concentration profiles measured in a lean (equivalence ratio 0.8), atmospheric pressure hydrogen–oxygen flame. The solid curve (absolute concentration) was calculated from the measured OH concentration, and the filled circles were measured by using optogalvanic spectroscopy (see Ref. 5). Two-step fluorescence spectroscopy was used to measure the relative profiles represented by the squares (1.0 mJ/pulse at 243 nm) and the triangles (2.1 mJ/pulse at 243 nm).

Fig. 4
Fig. 4

Dependences of the atomic hydrogen two-step fluorescence signal on 243-nm pulse energy measured in atmospheric pressure hydrogen–oxygen flames: circles, 1.3 mm above the burner in a rich (equivalence ratio 1.2) flame, triangles, 13 mm above the burner in a lean (equivalence ratio 0.8) flame. The dashed line passing through the circles has a slope of 2, consistent with an I 2 intensity dependence of the two-photon excitation process, and the dashed line passing through the triangles has a slope of 4, suggesting an additional I 2 intensity dependence for a photochemical production mechanism.

Fig. 5
Fig. 5

Top: spectrometer scan of the OH fluorescence excited by the 281-nm probe laser tuned to the (1,0)Q1(5) transition 120 ns after irradiating the flame gases by a 1.7-mJ 243-nm pulse tuned to the atomic hydrogen 1S–2S transition, demonstrating thermal equilibrium of the OH in the flame. Bottom: spectrometer scan of the OH emission produced by irradiating the flame gases by a 2.4-mJ 243-nm pulse tuned to the atomic hydrogen transition (probe laser blocked), showing emission from higher lying rotational levels of OH and strong atomic hydrogen 656-nm Balmer-α emission.

Fig. 6
Fig. 6

Measurement of the OH emission signal as the 243-nm pump beam was scanned across the atomic hydrogen 1S–2S transition. Top: OH fluorescence signal excited by the 281-nm probe beam; the dashed line represents the nascent OH fluorescence signal observed with the 243-nm beam blocked. Bottom: OH emission observed with only the 243-nm beam present. The same vertical units apply to both parts of the figure.

Fig. 7
Fig. 7

Dependences of the OH fluorescence probe signal on the pulse energy of the 243-nm pump beam: circles, 243-nm wavelength detuned from the atomic hydrogen 1S–2S transition; the dashed line has a slope of 2.0, consistent with an I 2 intensity dependence for the photochemical creation mechanism; triangles, 243-nm wavelength tuned onto the 1S–2S transition; the dashed line has a slope of 3.4, suggesting a higher-order photochemical creation mechanism; squares, simulation of on-resonance signal (displaced horizontally for clarity).

Fig. 8
Fig. 8

Dependence of the 656-nm atomic hydrogen emission on the pulse energy of a 243-nm beam tuned to the atomic hydrogen 1S–2S transition; the dashed line, with a slope of 6.4, represents a linear fit to the data points.

Equations (9)

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I LIF [ OH ] 0 + [ Δ OH ( t ) ] d t .
[ Δ OH ( t ) ] = k 1 I 2 ( t ) [ H 2 O ] + k 2 [ H 2 O ] [ H 2 S ( t ) ] ,
[ H 2 S ( t ) ] = k 3 I 2 ( t ) [ H 1 S ( t ) ] .
[ H 1 S ( t ) ] = [ H 1 S ] 0 + t k 1 I 2 ( τ ) [ H 2 O ] d τ .
I LIF [ OH ] 0 + ( k 1 [ H 2 O ] + k 2 k 3 [ H 2 O ]   [ H 1 S ] 0 ) I 2 ( t ) d t + k 1 k 2 k 3 [ H 2 O ] 2 { t I 2 ( τ ) d τ } I 2 ( t ) d t .
{ t f 2 ( τ ) d τ } f 2 ( t ) d t = ½ .
a ( k 1 + k 2 k 3 [ H 1 S ] 0 ) [ H 2 O ] ,
c k 1 k 2 k 3 [ H 2 O ] 2 ( k 1 + k 2 k 3 [ H 1 S ] 0 ) ,
I LIF [ OH ] 0 + a ( I 0 2 + c I 0 4 ) .

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