Abstract

A new method for the in situ detection of nonfluorescing molecular species is proposed: photofragmentation-laser induced fluorescence (PF-LIF). In this approach, the species to be detected is first laser photolyzed at a wavelength λ1, producing one or more vibrationally excited photofragments. Before vibrational relaxation occurs, one of these photofragments is pumped into a bonding excited state by a second laser pulse centered at wavelength λ2. Fluorescence is sampled at a wavelength λ3, where λ3 < λ2 and λ1. This pumping configuration thus permits massive discrimination against Rayleigh and Raman scattering as well as white noise fluorescence from the laser wavelengths λ1 and λ2. The technique should be both highly sensitive and selective for numerous atmospheric trace gases. Specific sampling schemes for detecting NO2, NO3, and HNO2 are proposed. Various noise sources and chemical interferences are discussed. Specific calculations that estimate the sensitivity of the PF-LIF system for detecting NO2, NO3, and HNO2 are given.

© 1980 Optical Society of America

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References

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  1. K. Sukurai, H. P. Broida, J. Chem. Phys. 50, 2404 (1969).
    [CrossRef]
  2. See, for example, W. M. Jackson, J. Chem. Phys. 50, 960 (1973); J. A. Silver, W. L. Dimpfl, J. H. Brophy, J. L. Kinsey, J. Chem. Phys. 65, 1811 (1976); J. A. Gelbwachs, M. Birnbaum, A. W. Tucker, C. L. Fincher, Opto-Electronics 4, 155 (1972).
    [CrossRef]
  3. D. D. Davis, W. S. Heaps, D. Philen, M. Rodgers, T. McGee, A. Nelson, A. J. Moriarty, Rev. Sci. Instrum. 50, No. 12, 70 (1979).
    [CrossRef]
  4. J. B. Halpern, W. M. Jackson, V. McCrary, Appl. Opt. 18, 590 (1979).
    [CrossRef] [PubMed]
  5. That is, having 1/e time constants for vibrational relaxation >1 μsec at atmospheric pressure.
  6. This also assumes that the RC time constant of the signal cable and related input-output detection electronics is <20 nsec.
  7. This will be true if two conditions are satisfied: (1) the signal lost in output signal gating is negligible; (2) impedance mismatches that result in reflections in the signal cable terminations are small so that, after two reflections, pulses on the signal cable are undetectable.
  8. Most diatomics have 1/e relaxation times from 5 to 20 times longer than this time delay.
  9. Interfering AB molecules might also be formed by secondary photochemistry involving the λ1 and/or λ2 laser beams.
  10. This technique of using vibrational and rotational population distributions to “fingerprint” molecules may have widespread use as an analytical tool for identification of species.
  11. E. R. Reiter, “The Natural Stratosphere of 1974,” CIAP Monograph I, DOT-TST-75-51 (1975).
  12. H. S. Johnston, R. A. Graham, J. Phys. Chem. 77, 62 (1973).
    [CrossRef]
  13. F. Magnotta, unpublished results (1979).
  14. R. A. Cox, J. Photochem. 3, 291 (1975).
    [CrossRef]
  15. R. A. Cox, J. Photochem. 3, 1975 (1975).
  16. In the (2,2) transition, k′ levels <15 want to be excited to prevent extensive predissociation of the OH.
  17. A. B. Callear, Proc. R. Soc. London Ser. A: 276, 401 (1963).
    [CrossRef]
  18. Extrapolated from the work of T. Tajime, T. Saheki, K. Ito, Appl. Opt. 17, 1290 (1978).
    [CrossRef] [PubMed]
  19. Corresponding to an assumed natural radiative lifetime of 160 nsec.
  20. G. Herzberg, Spectra of Diatomic Molecules (Van Nostrand Reinhold, New York, 1950).
  21. L. A. Melton, W. Klemperer, Planet. Space Sci. 20, 157 (1972).
    [CrossRef]
  22. U.S. Standard Atmosphere (U.S. GPO, Washington, D.C., 1966).
  23. R. J. Spindler, L. Isaacson, J. Wentink, J. Quant. Spectrosc. Radiat. Transfer 10, 621 (1970).
    [CrossRef]
  24. Estimated to be due principally to residual anti-Stokes Raman scattering from the λ2 laser beam.
  25. If the signal is assumed to follow a Poisson distribution, the standard deviation is given by σ=N, where N represents the total number of counts. This column thus gives the ratio of the signal to the statistical counting uncertainty.

1979 (2)

D. D. Davis, W. S. Heaps, D. Philen, M. Rodgers, T. McGee, A. Nelson, A. J. Moriarty, Rev. Sci. Instrum. 50, No. 12, 70 (1979).
[CrossRef]

J. B. Halpern, W. M. Jackson, V. McCrary, Appl. Opt. 18, 590 (1979).
[CrossRef] [PubMed]

1978 (1)

1975 (2)

R. A. Cox, J. Photochem. 3, 291 (1975).
[CrossRef]

R. A. Cox, J. Photochem. 3, 1975 (1975).

1973 (2)

H. S. Johnston, R. A. Graham, J. Phys. Chem. 77, 62 (1973).
[CrossRef]

See, for example, W. M. Jackson, J. Chem. Phys. 50, 960 (1973); J. A. Silver, W. L. Dimpfl, J. H. Brophy, J. L. Kinsey, J. Chem. Phys. 65, 1811 (1976); J. A. Gelbwachs, M. Birnbaum, A. W. Tucker, C. L. Fincher, Opto-Electronics 4, 155 (1972).
[CrossRef]

1972 (1)

L. A. Melton, W. Klemperer, Planet. Space Sci. 20, 157 (1972).
[CrossRef]

1970 (1)

R. J. Spindler, L. Isaacson, J. Wentink, J. Quant. Spectrosc. Radiat. Transfer 10, 621 (1970).
[CrossRef]

1969 (1)

K. Sukurai, H. P. Broida, J. Chem. Phys. 50, 2404 (1969).
[CrossRef]

1963 (1)

A. B. Callear, Proc. R. Soc. London Ser. A: 276, 401 (1963).
[CrossRef]

Broida, H. P.

K. Sukurai, H. P. Broida, J. Chem. Phys. 50, 2404 (1969).
[CrossRef]

Callear, A. B.

A. B. Callear, Proc. R. Soc. London Ser. A: 276, 401 (1963).
[CrossRef]

Cox, R. A.

R. A. Cox, J. Photochem. 3, 291 (1975).
[CrossRef]

R. A. Cox, J. Photochem. 3, 1975 (1975).

Davis, D. D.

D. D. Davis, W. S. Heaps, D. Philen, M. Rodgers, T. McGee, A. Nelson, A. J. Moriarty, Rev. Sci. Instrum. 50, No. 12, 70 (1979).
[CrossRef]

Graham, R. A.

H. S. Johnston, R. A. Graham, J. Phys. Chem. 77, 62 (1973).
[CrossRef]

Halpern, J. B.

Heaps, W. S.

D. D. Davis, W. S. Heaps, D. Philen, M. Rodgers, T. McGee, A. Nelson, A. J. Moriarty, Rev. Sci. Instrum. 50, No. 12, 70 (1979).
[CrossRef]

Herzberg, G.

G. Herzberg, Spectra of Diatomic Molecules (Van Nostrand Reinhold, New York, 1950).

Isaacson, L.

R. J. Spindler, L. Isaacson, J. Wentink, J. Quant. Spectrosc. Radiat. Transfer 10, 621 (1970).
[CrossRef]

Ito, K.

Jackson, W. M.

J. B. Halpern, W. M. Jackson, V. McCrary, Appl. Opt. 18, 590 (1979).
[CrossRef] [PubMed]

See, for example, W. M. Jackson, J. Chem. Phys. 50, 960 (1973); J. A. Silver, W. L. Dimpfl, J. H. Brophy, J. L. Kinsey, J. Chem. Phys. 65, 1811 (1976); J. A. Gelbwachs, M. Birnbaum, A. W. Tucker, C. L. Fincher, Opto-Electronics 4, 155 (1972).
[CrossRef]

Johnston, H. S.

H. S. Johnston, R. A. Graham, J. Phys. Chem. 77, 62 (1973).
[CrossRef]

Klemperer, W.

L. A. Melton, W. Klemperer, Planet. Space Sci. 20, 157 (1972).
[CrossRef]

Magnotta, F.

F. Magnotta, unpublished results (1979).

McCrary, V.

McGee, T.

D. D. Davis, W. S. Heaps, D. Philen, M. Rodgers, T. McGee, A. Nelson, A. J. Moriarty, Rev. Sci. Instrum. 50, No. 12, 70 (1979).
[CrossRef]

Melton, L. A.

L. A. Melton, W. Klemperer, Planet. Space Sci. 20, 157 (1972).
[CrossRef]

Moriarty, A. J.

D. D. Davis, W. S. Heaps, D. Philen, M. Rodgers, T. McGee, A. Nelson, A. J. Moriarty, Rev. Sci. Instrum. 50, No. 12, 70 (1979).
[CrossRef]

Nelson, A.

D. D. Davis, W. S. Heaps, D. Philen, M. Rodgers, T. McGee, A. Nelson, A. J. Moriarty, Rev. Sci. Instrum. 50, No. 12, 70 (1979).
[CrossRef]

Philen, D.

D. D. Davis, W. S. Heaps, D. Philen, M. Rodgers, T. McGee, A. Nelson, A. J. Moriarty, Rev. Sci. Instrum. 50, No. 12, 70 (1979).
[CrossRef]

Reiter, E. R.

E. R. Reiter, “The Natural Stratosphere of 1974,” CIAP Monograph I, DOT-TST-75-51 (1975).

Rodgers, M.

D. D. Davis, W. S. Heaps, D. Philen, M. Rodgers, T. McGee, A. Nelson, A. J. Moriarty, Rev. Sci. Instrum. 50, No. 12, 70 (1979).
[CrossRef]

Saheki, T.

Spindler, R. J.

R. J. Spindler, L. Isaacson, J. Wentink, J. Quant. Spectrosc. Radiat. Transfer 10, 621 (1970).
[CrossRef]

Sukurai, K.

K. Sukurai, H. P. Broida, J. Chem. Phys. 50, 2404 (1969).
[CrossRef]

Tajime, T.

Wentink, J.

R. J. Spindler, L. Isaacson, J. Wentink, J. Quant. Spectrosc. Radiat. Transfer 10, 621 (1970).
[CrossRef]

Appl. Opt. (2)

J. Chem. Phys. (2)

K. Sukurai, H. P. Broida, J. Chem. Phys. 50, 2404 (1969).
[CrossRef]

See, for example, W. M. Jackson, J. Chem. Phys. 50, 960 (1973); J. A. Silver, W. L. Dimpfl, J. H. Brophy, J. L. Kinsey, J. Chem. Phys. 65, 1811 (1976); J. A. Gelbwachs, M. Birnbaum, A. W. Tucker, C. L. Fincher, Opto-Electronics 4, 155 (1972).
[CrossRef]

J. Photochem. (2)

R. A. Cox, J. Photochem. 3, 291 (1975).
[CrossRef]

R. A. Cox, J. Photochem. 3, 1975 (1975).

J. Phys. Chem. (1)

H. S. Johnston, R. A. Graham, J. Phys. Chem. 77, 62 (1973).
[CrossRef]

J. Quant. Spectrosc. Radiat. Transfer (1)

R. J. Spindler, L. Isaacson, J. Wentink, J. Quant. Spectrosc. Radiat. Transfer 10, 621 (1970).
[CrossRef]

Planet. Space Sci. (1)

L. A. Melton, W. Klemperer, Planet. Space Sci. 20, 157 (1972).
[CrossRef]

Proc. R. Soc. London Ser. A (1)

A. B. Callear, Proc. R. Soc. London Ser. A: 276, 401 (1963).
[CrossRef]

Rev. Sci. Instrum. (1)

D. D. Davis, W. S. Heaps, D. Philen, M. Rodgers, T. McGee, A. Nelson, A. J. Moriarty, Rev. Sci. Instrum. 50, No. 12, 70 (1979).
[CrossRef]

Other (14)

Corresponding to an assumed natural radiative lifetime of 160 nsec.

G. Herzberg, Spectra of Diatomic Molecules (Van Nostrand Reinhold, New York, 1950).

U.S. Standard Atmosphere (U.S. GPO, Washington, D.C., 1966).

Estimated to be due principally to residual anti-Stokes Raman scattering from the λ2 laser beam.

If the signal is assumed to follow a Poisson distribution, the standard deviation is given by σ=N, where N represents the total number of counts. This column thus gives the ratio of the signal to the statistical counting uncertainty.

F. Magnotta, unpublished results (1979).

In the (2,2) transition, k′ levels <15 want to be excited to prevent extensive predissociation of the OH.

That is, having 1/e time constants for vibrational relaxation >1 μsec at atmospheric pressure.

This also assumes that the RC time constant of the signal cable and related input-output detection electronics is <20 nsec.

This will be true if two conditions are satisfied: (1) the signal lost in output signal gating is negligible; (2) impedance mismatches that result in reflections in the signal cable terminations are small so that, after two reflections, pulses on the signal cable are undetectable.

Most diatomics have 1/e relaxation times from 5 to 20 times longer than this time delay.

Interfering AB molecules might also be formed by secondary photochemistry involving the λ1 and/or λ2 laser beams.

This technique of using vibrational and rotational population distributions to “fingerprint” molecules may have widespread use as an analytical tool for identification of species.

E. R. Reiter, “The Natural Stratosphere of 1974,” CIAP Monograph I, DOT-TST-75-51 (1975).

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Figures (2)

Fig. 1
Fig. 1

OH energy diagram showing LIF pumping and sampling scheme.

Fig. 2
Fig. 2

Wavelength detection scheme of PF-LIF technique.

Tables (3)

Tables Icon

Table I Estimation of E λ 2, Ef, Ed, Ee, and V for Detection of NO2, NO3, and HNO2

Tables Icon

Table II Estimation of E λ 1 for Detection of Three NOx Species

Tables Icon

Table III PF-LIF Signals for Detection of Three NOx Species

Equations (22)

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D λ 3 = ( total number of λ 3 photons emitted P λ 3 ) × ( optical detection efficiency for λ 3 photons E d ) × ( electronic detection efficiency E e ) .
D λ 3 = P λ 3 × E d × E e .
E e = ( PMT signal pulses counted P d ) ( PMT signal pulses emitted P s ) .
E d = ( fraction of total fluorescence at sampling wavelength λ 3 , γ λ 3 ) × ( collection optics efficiency factor at λ 3 , Y λ 3 ) × ( filter transmission factor at λ 3 , Z λ ) × ( quantum efficiency of PMT , ϕ λ 3 ) ,
E d = γ λ 3 × Y λ 3 × Z λ 3 × ϕ λ 3 .
P λ 3 = ( total number of λ 2 photons absorbed N λ 2 ) × ( fluorescence efficiency E f ) .
N λ 2 = ( total number of A B molecules in quantum state i within sampling region C i ) × ( fraction of molecules in quantum state i absorbing photons E λ 2 ) .
C i = ( number of A B C molecules in sampling region C x ) × ( fraction of A B C molecules undergoing photolysis and producing photofragments in quantum state i E λ 1 ) .
C x = ( volume of sampling region V ) × ( concentration of the precursor species [ A B C ] ) .
V = a λ 1 × l ,
E λ = [ 1 exp ( P λ 1 σ λ 1 a λ 1 ) ] × Q x × f i × F .
E λ 2 = P λ 2 × σ λ 2 a λ 2 × a λ 2 a λ 1 ,
E f = ( fraction of excited molecules producing fluorescence ) = k f [ k f + k d + k q [ M ] ] ,
P λ 3 = E λ 1 × E λ 2 × E f × V × [ A B C ] .
D λ 3 = E λ 1 × E λ 2 × E f × E d × E e × V × [ A B C ] .
E λ 1 = ( photolysis efficiency at λ 1 ) = [ 1 exp ( P λ 1 σ λ 1 a λ 1 ) ] × f i × F ; E λ 2 = ( optical pumping efficiency at λ 2 ) = P λ 2 × σ λ 2 a λ 2 × ( a λ 2 a λ 1 ) ; E f = ( fluorescence efficiency ) = [ k f ] [ k f + k d + k q [ M ] ] ; E d = ( optical detection efficiency ) = γ λ 3 × Y λ 3 × Z λ 3 × ϕ λ 3 ; E = ( electronic detection efficiency ) = P d P s ; V = ( volume of sampling region ) = a λ 1 × l .
( P λ 1 P λ 2 ¯ ) ( P λ 1 ¯ ) × ( P λ 2 ¯ ) ,
( a ) A B 2 + h ν 2 [ A B 2 ] h ν 2 A B * 2 A B * 2 A B 2 + h ν 3 ( ν 3 > ν 2 ) , ( b ) A C 2 + h ν 2 A C * 2 h ν 2 A C 2 * * A C 2 * * A C 2 + h ν 4 ( ν 4 > ν 2 ) , ( c ) A C 2 + h ν 2 A C * 2 M A C 2 A C 2 + h ν 2 A C 2 * A C 2 + h ν 5 ( ν 5 > ν 2 ) , ( d ) A C + h ν 2 A C * 2 A C 2 + h ν 6 ( ν 6 < ν 2 ) A C 2 + h ν 2 A C 2 * A C 2 + h ν 7 ( ν 7 > ν 2 ) , ( e ) A D 2 + h ν 2 A D * 2 h ν 2 A D * + D A D * A D + h ν 8 ( ν 8 > ν 2 ) .
( a ) NO 2 + h ν 1 ( λ 1 = 300 nm ) NO ( X 2 Π , υ = 2 ) + 0 ( 3 P ) , ( b ) NO ( υ = 2 ) + h ν 2 ( λ 2 = 248 nm ) NO ( A 2 Σ + , υ = 0 ) , ( c ) NO ( A 2 Σ + , υ = 0 ) NO ( X 2 Π , υ = 0 ) + h ν 3 ( λ 3 = 226 nm ) .
( d ) NO 3 + h ν ( λ 1 = 589 nm ) NO ( X 2 Π , υ = 2 ) + 0 2 ( 1 Δ )
( e ) HNO 2 + h ν ( λ 1 = 355 nm ) NO ( X 2 Π , υ = 2 ) + OH ( X 2 Π )
D λ 3 = 1.1 × 10 12 cm 3 × [ NO 2 ] , D λ 3 = 2.5 × 10 12 cm 3 × [ HNO 2 ] , D λ 3 = 9.9 × 10 11 cm 3 × [ NO 3 ] .

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