Luisa T. Molina and William B. Grant, "FTIR-spectrometer-determined absorption coefficients of seven hydrazine fuel gases: implications for laser remote sensing," Appl. Opt. 23, 3893-3900 (1984)
The absorption spectra of three hydrazines and four of their air-oxidation products were measured in the 9–12-μm spectral region with a Fourier transform infrared (FTIR) spectrometer with a 0.05-cm−1 resolution to determine absorption coefficients at CO2 and tunable diode laser wavelengths. The measurements agreed well with published CO2 laser determinations for many of the absorption coefficients, except where the published values are thought to be in error. The coefficients were then used to estimate the sensitivity for remote detection of these gases using CO2 and tunable diode lasers in long-path differential absorption measurements.
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α(X) is the value of the absorption coefficient reported in Ref. X. αFTIR is the value measured using the FTIR spectrometer at JPL.
ΔαFTIR is the standard deviation of these values.
atm−1 cm−1.
Average of six measurements with NH3 pressure varied from 0.53 to 2.9 Torr buffered with N2 to 760 Torr. Resolution = 0.05 cm−1.
These frequencies appear between two strong NH3 absorption features.
Table II
Comparison of Gas Absorption Coefficients at CO2 Laser Frequencies Determined Using an FTIR Spectrometer with Those Using CO2 Lasera,b
The values determined using a CO2 laser are from Ref. 12. Each value is an average for approximately 5–15 absorption coefficients.
The authors of Ref. 12 have recently remeasure the UDMH absorption coefficient resulting in a new ratio of 1.25 ± 0.10.
Table III
Comparison of Absorption Coefficients for the Hydrazines Determined In Three Laboratoriesa
Only the maximum differential absorptance in a region up to 0.5 cm−1 was used in the calculation, since that is a typical single-mode operating range for TDLs, even though the absorption line may have a larger width.
Sensitivity assumed for differential absorptances is 3 × 10−4.
Table VII
Estimated Sensitivities for Frequency-Modulation Spectroscopy Measurements of Hydrazine Fuel Gasesa
Gas
Laser frequency (cm−1)
Differential absorption coefficient (atm−1 cm−1)
Estimated measurement sensitivity (ppm-m)
N2H4
924.97
1.33
1.1
MMH
967.71
0.65
2.3
UDMH
931.00
0.05
30.
NH3
1084.64
7.54
0.20
MeOH
1033.49
0.87
1.7
DMA
—
TMA
1046.85
0.024
62.
Assumed sensitivity is 3 × 10−4 with sidebands at ±1 GHz.
Tables (7)
Table I
NH3 Absorption Coefficients at CO2 Laser Frequenciesa
α(X) is the value of the absorption coefficient reported in Ref. X. αFTIR is the value measured using the FTIR spectrometer at JPL.
ΔαFTIR is the standard deviation of these values.
atm−1 cm−1.
Average of six measurements with NH3 pressure varied from 0.53 to 2.9 Torr buffered with N2 to 760 Torr. Resolution = 0.05 cm−1.
These frequencies appear between two strong NH3 absorption features.
Table II
Comparison of Gas Absorption Coefficients at CO2 Laser Frequencies Determined Using an FTIR Spectrometer with Those Using CO2 Lasera,b
The values determined using a CO2 laser are from Ref. 12. Each value is an average for approximately 5–15 absorption coefficients.
The authors of Ref. 12 have recently remeasure the UDMH absorption coefficient resulting in a new ratio of 1.25 ± 0.10.
Table III
Comparison of Absorption Coefficients for the Hydrazines Determined In Three Laboratoriesa
Only the maximum differential absorptance in a region up to 0.5 cm−1 was used in the calculation, since that is a typical single-mode operating range for TDLs, even though the absorption line may have a larger width.
Sensitivity assumed for differential absorptances is 3 × 10−4.
Table VII
Estimated Sensitivities for Frequency-Modulation Spectroscopy Measurements of Hydrazine Fuel Gasesa
Gas
Laser frequency (cm−1)
Differential absorption coefficient (atm−1 cm−1)
Estimated measurement sensitivity (ppm-m)
N2H4
924.97
1.33
1.1
MMH
967.71
0.65
2.3
UDMH
931.00
0.05
30.
NH3
1084.64
7.54
0.20
MeOH
1033.49
0.87
1.7
DMA
—
TMA
1046.85
0.024
62.
Assumed sensitivity is 3 × 10−4 with sidebands at ±1 GHz.
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