Opto-galvanic detection of species in flames

Green, R. B.; Keller, R.; Schenck, Peter K.; Travis, John C.; Luther, G. G.

doi:10.1021/ja00442a035

Cited by 101 publications

(30 citation statements)

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“…A number of workers have reported ionization phenomena following laser excitation and the term "optogalvanic effect" is sometimes used in this connection [5][6][7][8][9]. Related experiments are reported in [1,10], which deal with two-photon excitation and the resulting population redistribution among the higher levels of Na atoms in an H2-O2-Ar flame.…”

Section: Introductionmentioning

confidence: 99%

Collisional ionization of Na atoms excited by one- and two-photon absorption in H2O2Ar flames

Dijk

Alkemade

1980

Combustion and Flame

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An ionization signal was detected when a flashlamp-pumped dye laser was tuned on resonance with various one-or two-photon transitions of Na atoms in an H~_--O2-Ar flume of 1800 K at atmospheric pressure. Ionization signals were obtained by collecting the electric charge with two thin iridium probes which were immersed into the flume. Relative ionization signals were measured as a function of dc probe voltage, laser tuning, Na-solution concentration, and free-O~ concentration. Fluorescence signals served to monitor the relative populations of the higher Na levels. A preliminary qualitative interpretation is given on the basis of collisional ionization from the saturated as well as the higher levels, which are mutually connected by population redistribution. With the assumption of a quasi-steady-state ionization, an effective Saha equation is derived, which connects the concentration of the atoms in the saturated level with the ionic concentration by an effective ionization constant. Values of this constant were estimated from the experiments and compared for the different excitation modi investigated. Additional one-photon wing excitation of the 3P-5S transition might play a role as an intermediate step in the ion production when the 3P level is saturated. The presence of excess O_~ molecules enhances the degree of ionization, whereas the addition of comparable quantities of N 2 molecules does not have this effect. This is explained by the positive electron affinity of O~, which shifts the effective ionization equilibrium. The role of multiphoton processes which directly transfer Na atoms from the 3S or 3P state to the continuum state is shown to be negligible. Also the role played by the associative ionization reaction: Na(3P) + Nal3P) ~ Na + + e--is shown to be negligible under our experimental conditions.

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Section: Introductionmentioning

confidence: 99%

Collisional ionization of Na atoms excited by one- and two-photon absorption in H2O2Ar flames

Dijk

Alkemade

1980

Combustion and Flame

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“…The laser-related current pulse is detected with electrodes and monitored with conventional electronics. LEI, a special case of the optogalvanic effect ( I ) , has been directed toward analytical flame spectrometry (2)(3)(4)(5)(6)(7)(8)(9)(10)(11).…”

Section: Depattment Of Chemistry Chemistry Building University Of Amentioning

confidence: 99%

Acid effects in laser-enhanced ionization spectrometry

Trask¹,

Green²

1981

Anal. Chem.

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Mineral acids are often added to samples prior to flame spectrometric determinations. Mineral acids produce enhancement and suppression of analyte slgnals In laser-enhanced loniratlon (LEI) spectrometry. Thls paper characterizes these effects, examines them in detall, and provides explanations for the observed slgnal behavior. The addition of nitric acid to standard and sample solutions is suggested as a means of improving LEI signals while preventing adsorption on container walls durlng storage.

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“…The laser-enhanced ionization technique (LED as an application of the optogalvanic effect to flames was first developed in 1976 and has, since then, demonstrated its potential in detecting traces. [1][2][3] In some elements, for instance, LEI has been employed in order to achieve a detection limit as low as 0.001 ppb (ng/mL)2 It has also been used to determine flame temperature, the amount of produced ion yield, and radical structures. 4-7 To achieve optimal sensitivity and selectivity in trace detection, meanwhile, researchers have been conducting studies of the characteristics of the ion signal, electrical interference, electrode design, and ion collection configuration, as well as the influence of the space charge and the bias voltage on collection efficiency, s-14…”

Section: Introductionmentioning

confidence: 99%

Ion Enhancement by Dual-Laser Ionization in an Acetylene/Air Flame

Lin

Duh

1989

Appl Spectrosc

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A technique of dual-laser ionization (DLI) is employed to detect Na trace released in an acetylene/air flame. In comparison with laser-enhanced ionization (LEI), a measurement of ion enhancement by the DLI method is found to be as large as two orders of magnitude. The ratio of DLI/LEI depends upon various factors, such as the second-step transition probability, the laser intensity, the transition linewidth, and the collisional ionization rate involved in the LEI mechanism. However, the relative ion enhancement with respect to the various second-step excitations is largely dominated by the ratio of the corresponding second-step transition probability. On the basis of this factor, a comparison between observation and estimation is found to be in satisfactory agreement.

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Opto-galvanic detection of species in flames

Cited by 101 publications

References 0 publications

Collisional ionization of Na atoms excited by one- and two-photon absorption in H2O2Ar flames

Collisional ionization of Na atoms excited by one- and two-photon absorption in H2O2Ar flames

Acid effects in laser-enhanced ionization spectrometry

Ion Enhancement by Dual-Laser Ionization in an Acetylene/Air Flame

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