20th AIAA Advanced Measurement and Ground Testing Technology Conference, 1998
Three infrared diagnostic techniques are developed to characterize chemical contamination in wind... more Three infrared diagnostic techniques are developed to characterize chemical contamination in wind tunnels and shock tubes which can affect the reliability of infrared sensor and imaging system tests. The techniques are based on mid-infrared spectroscopy, since the primary interest is in contaminants with mid-infrared emission or absorption spectra overlapping spectral windows of HgCdTe and InSbbased detectors. The first technique consists of collecting a sample of the pre-expansion wind-tunnel or shock-tube feedstock gas stream and then analyzing the sample with long-optical-pathlength, high-spectral-resolution, Fourier-transform infrared (FTIR) spectroscopy. The technique has the capability of giving a broad survey of potential chemical contaminates in the flow stream, but suffers from the inability to characterize contaminates which form during the blow-down process. The second technique captures a sample of the windtunnel or shock-tube blow-down gas stream for analysis by FTIR spectroscopy. This technique gives more detailed information about the contamination than the presampling technique, but does not have the ability to detect highly reactive or unstable contaminants. Also, little information is obtained about the temporal profile of the contaminants during the blow-down process. The third technique uses a rapidscan mid-infrared diode-laser spectrometer to record the in situ mid-infrared absorption spectrum of a specific chemical contaminant in the wind tunnel or shock tube. In its present configuration, the diode-laser spectrometer has a time resolution of approximately 100 ms. The three techniques are demonstrated using the Mach 8 wind-tunnel facility at Princeton University and the Hypervelocity Wind Tunnel 9 Facility at White Oaks, Maryland.
Evaluation of Fouriertransform microwave spectroscopy as a tool for quantitative analysis: signal stability considerations
There is a continuing need for improved analytical techniques to measure the concentration of tra... more There is a continuing need for improved analytical techniques to measure the concentration of trace gases for monitoring hazardous air pollutants, industrial emissions, chemical-warfare agent release, etc. Methods of analysis that can conclusively identify several analytes in a mixture are particularly desired. Towards this end, the use of Fourier-transform microwave (FTMW) spectroscopy as a quantitative analytical technique has been proposed.
Submillimeter Absorption Spectroscopy of the ICP-GEC Reference Cell
Millimeter and submillimeter (100 GHz to 1 THz) absorption spectroscopy is being developed as a s... more Millimeter and submillimeter (100 GHz to 1 THz) absorption spectroscopy is being developed as a sensor for measuring radical densities and temperatures in processing plasmas for microelectronics. Most molecules, radicals, and ions have transitions suitable for detection at these frequencies and the necessary spectroscopic data is available in the literature for determining the absolute radical densities. In addition, the narrow
A proposed global atmospheric monitoring network based on standard stars
Proceedings of Spie the International Society For Optical Engineering, Aug 1, 2009
The feasibility of developing a network of telescopes to monitor the composition of the nighttime... more The feasibility of developing a network of telescopes to monitor the composition of the nighttime atmosphere using stellar spectrophotometry is explored. Spectral measurements of the extinction of starlight by the atmosphere would allow, for instance, quantification of aerosol, cloud, water-vapor, and ozone levels over the full range of elevation and azimuth. These measurements, when combined with data from solar spectrophotometry
were recorded using a pulsed molecular beam Fourier transform microwave spectrometer. The K ϭ 0 a... more were recorded using a pulsed molecular beam Fourier transform microwave spectrometer. The K ϭ 0 and K ϭ 1 components of the J ϭ 3 4 2 through the J ϭ 7 4 6 transitions were measured and assigned in the 9-24 GHz region. For the primary 28 Si isotopic species, Ar-28 SiH 4 and Ar-28 SiD 4 , a K ϭ 0, A symmetry, a K ϭ 0, F symmetry, a doubly degenerate K ϭ 1, E symmetry, and an l/K-doubled, K ϭ 1, F symmetry rotational progression are observed at the Ϸ1 K rotational temperature of the supersonic expansion. The rotational constants for the K ϭ 0, A state for Ar-28 SiH 4 and Ar-28 SiD 4 are B ϭ 1700.40624(9) MHz and 1630.687073(22) MHz and the centrifugal distortion constants are D J ϭ 29.089(3) and 20.0198(8) kHz and H J ϭ Ϫ1.91(3) and Ϫ0.851(8) Hz, respectively, where type A expanded uncertainties with a coverage factor, k ϭ 3, are given here and elsewhere. The values of the rotational constants for the K ϭ 0, A, and F states and for the K ϭ 1, E state are in good agreement with the infrared-determined values for Ar-28 SiH 4. The measured linear Stark effect of the Estate transitions was analyzed to give a dipole moment of 9.24(8) ϫ 10 Ϫ32 C ⅐ m [0.0277(2) D].
NIST Response to the 6th CORM Report: Pressing Problems and Projected National Needs in Optical Radiometry
Nasa Sti Recon Technical Report N, Nov 1, 2001
ABSTRACT The Council for Optical Radiation Measurements (CORM) issues periodic reports relevant t... more ABSTRACT The Council for Optical Radiation Measurements (CORM) issues periodic reports relevant to the mission of the Optical Technology Division of the Physics Laboratory. The present document summarizes NIST's response to the CORM Sixth Report issued in 1995 and is timed to be contemporary with the CORM Seventh Report to be issued in 2001.
The radio frequency and microwave spectra of NH3-C02 have been measured using the molecular beam electric resonance technique. The spectrum is characteristic of an asymmetric top in which the NH3 subunit exhibits effectively free internal rotation. The spectroscopic constants obtained for the gro...
The radio frequency and microwave spectra of NH3–CO2 have been measured using the molecular beam ... more The radio frequency and microwave spectra of NH3–CO2 have been measured using the molecular beam electric resonance technique. The spectrum is characteristic of an asymmetric top in which the NH3 subunit exhibits effectively free internal rotation. The spectroscopic constants obtained for the ground internal rotor state are presented below: (B+C/2) (MHz) 3756.178(3), (B−C/2) (MHz) 597.4(2), A−(B+C/2) (MHz) 8035.(8), ΔJ (MHz) 0.0240(4), δK (MHz) 0.20(2), ΔJK (MHz) 0.23(5), δJ (MHz) 0.007(1), eQqaa (MHz) −3.175(4), eQqbb (MHz) 1.557(9), eQqcc (MHz) 1.617(11), μ(D) 1.7684(14). The N–CO2 framework of the complex has C2v symmetry with a N–C weak bond length of 2.9875(4) A˚. The average bending angle of the NH3 subunit is 22.71(5)° with a difference in amplitude of 1.0(4)° between the in plane and out of plane excursions. The weak bond stretching force constant is 0.070(1) mdyn/A˚ and the induced dipole moment is 0.411(2) D. (B+C)/2 for the first excited internal rotor state (‖m‖=1) is 3753.008(4) MHz and the quadrupole coupling constant eQq‖m‖=1aa=−3.176(9) MHz is identical with that measured for the ground internal rotor state.
Investigation of collision-induced absorption in the vibrational fundamental bands of O2 and N2 at elevated temperatures
J Mol Spectrosc, 2005
ABSTRACT Collision-induced absorption has been measured for the vibrational fundamental bands of ... more ABSTRACT Collision-induced absorption has been measured for the vibrational fundamental bands of N2 and O2 at temperatures up to 360K. These data when combined with previously obtained lower temperature data show that the integrated band intensity of the O2 fundamental increases as the temperature is raised above 300K. The integrated intensity of the N2 band also increases, but at a much lower rate with temperature.
The intensities of the collision-induced absorption (CIA) bands associated with the electric-dipo... more The intensities of the collision-induced absorption (CIA) bands associated with the electric-dipole forbidden O 2 fundamental and the CO 2 m 1 =2m 2 Fermi dyad monomer vibrational bands have been studied over the temperature range 193-360 K and the frequency range 1100-2000 cm À1. As CO 2 is added to a pure O 2 sample, the intensity in the O 2 fundamental band region increases dramatically. At the lowest temperature studied, 193 K, the band-integrated CIA coefficient for enhancement of the Fermi dyad absorption from CO 2 to CO 2 collisions, S CO2-CO2 , is more than a factor of two larger than the band-integrated CIA coefficient for enhancement of the O 2 vibrational fundamental by CO 2 collisions, S O2-CO2. Moreover, the S CO2-CO2 coefficient shows a significantly larger temperature dependence, increasing by more than a factor of two from 345.6 to 193 K while S O2-CO2 increases by less than one third. The band shapes and their temperature dependence provide clear evidence for the formation of CO 2-CO 2 and CO 2-O 2 complexes. The CO 2-CO 2 dimer feature is most striking, contributing significantly to the infrared absorption near the expected CO 2 monomer fundamentals. Evidence for the more weakly bound CO 2-O 2 complex is seen on the O 2 CIA band, particularly at the lowest temperatures studied. The shapes for both dimer bands display sharp a-type Q branch central profiles and broad P and R branch like structure attributed to b-type Q branches for the CO 2-CO 2 complex and a-type P and R branch structure for the CO 2-O 2 complex. The present results stress the importance of including bound and metastable dimer absorption in any theoretical modeling of CIA, particularly when one of the collision partners has a large electrostatic moment, such as CO 2 with its large electric quadrupole moment.
We measured at 296 K the rotational line strengths and pressure-broadening coefficients for the 1... more We measured at 296 K the rotational line strengths and pressure-broadening coefficients for the 1.27-m, a 1 ⌬ g-X 3 ⌺ g Ϫ , v ϭ 0-0 band of O 2 with a Fourier transform infrared spectrometer using an optical path length of 84 m, a spectral resolution of 0.01 cm Ϫ1 , and sample pressures between 13 and 104 kPa. The integrated band strength is 7.79͑17͒ ϫ 10 Ϫ6 m Ϫ2 Pa Ϫ1 ͓7.89͑17͒ ϫ 10 Ϫ5 cm Ϫ2 atm Ϫ1 ͔, and the Einstein A coefficient for spontaneous emission is 2.237͑51͒ ϫ 10 Ϫ4 s Ϫ1 , which corresponds to an upper-state 1͞e lifetime of 1.24͑3͒ h. The pressure-broadening coefficients decrease with increasing N and range from 19 to 38 MHz͞kPa ͑FWHM͒. The mean value for the transitions studied is 30.3͑21͒ MHz͞kPa ͓0.1024͑71͒ cm Ϫ1 ͞atm͔ ͑FWHM͒. The Einstein A coefficient determined here is in good agreement with the widely accepted value of 2.58 ϫ 10 Ϫ4 s Ϫ1 initially obtained by Badger et al. ͓J. Chem. Phys. 43, 4345 ͑1965͔͒ more than 30 years ago. The standard uncertainties given above are one standard deviation.
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