Water Vapor Absorption Measurements Research Articles

Versatile OSCAT time-domain THz spectrometer.

We report on a compact and versatile time-domain spectrometer operating in the THz spectral region from 0.2 to 2.5 THz based on ultrafast Yb:CALGO laser and photo-conductive antennas. The spectrometer operates with the optical sampling by cavity tuning (OSCAT) method based on laser repetition rate tuning, which allows at the same time the implementation of a delay-time modulation scheme. The whole characterization of the instrument is presented and compared to the classical THz time-domain spectroscopy implementation. THz spectroscopic measurements on a 520-μm thick GaAs wafer substrate together with water vapor absorption measurements are also reported to further validate the instrument capabilities.

Upper limits for absorption by water vapor in the near-UV

There are few experimental measurements of absorption by water vapor in the near-UV. Here we report the results of spectral measurements of water vapor absorption at ambient temperature and pressure from 325nm to 420nm, covering most tropospherically relevant short wavelengths. Spectra were recorded using a broadband optical cavity in the chemically controlled environment of an atmospheric simulation chamber. No absorption attributable to the water monomer (or the dimer) was observed at the 0.5nm resolution of our system. Our results are consistent with calculated spectra and recent DOAS field observations, but contradict a report of significant water absorption in the near-UV. Based on the detection limit of our instrument, we report upper limits for the water absorption cross section of less than 5×10−26cm2molecule−1 at our instrument resolution. For a typical, indicative slant column density of 4×1023cm2, we calculate a maximum optical depth of 0.02 arising from absorption of water vapor in the atmosphere at wavelengths between 340nm and 420nm, with slightly higher maximum optical depths below 340nm. The results of this work, together with recent atmospheric observations and computational results, suggest that water vapor absorption across most of the near-UV is small compared to visible and infrared wavelengths.

Effects of water vapor absorption on the physical and chemical stability of amorphous sodium indomethacin

This study reports on the effects that water absorbed into amorphous sodium indomethacin (NaIMC) can have on simultaneous tendencies to crystallize to its trihydrate form and to undergo base-catalyzed hydrolysis because of the plasticizing effects of water on molecular mobility. Measurement of water vapor absorption at 30 degrees C and powder x-ray diffraction patterns as a function of relative humidity (RH) reveal that upon exposure to 21% RH, NaIMC does not crystallize over a 2-month period. Measurements of the glass transition temperature as a function of such exposure reveals a change in T(g) from 121 degrees C, dry, to 53 degrees C at 21% RH, such that T(g) at 21% RH is approximately 13 degrees C above the highest storage temperature of 40 degrees C used in the study. At 56% RH and higher, however, crystallization to the trihydrate occurs rapidly; although over the 2-month period, crystallization was never complete. Assessment of chemical degradation by high-performance liquid chromatography analysis revealed significant instability at 21% RH; whereas at higher RH, the extent of chemical degradation was reduced, reflecting the greater crystallization to the more chemically stable crystalline form. It is concluded that when amorphous forms of salts occur in solid dosage forms, the simultaneous effects of enhanced water vapor sorption on crystallization and chemical degradation must be considered, particularly when assessing solid-state chemical degradation at higher temperatures and RH (eg, 40 degrees C 75% RH).

Extinction and Sky Brightness at Two Solar Observatories

The Advanced Technology Solar Telescope site survey Sky Brightness Monitor simultaneously images the solar disk and the sky to about 8 solar radii in four wavelengths at 450, 530, 890 and 940 nm. One day of data from Mees Solar Observatory on Haleakala and from the National Solar Observatory at Sacramento Peak (Sunspot, New Mexico) are analyzed. Both sites show strong Rayleigh extinction, but while Haleakala shows a larger aerosol component, Sunspot shows a large variation in the aerosol component. Overall the Haleakala extinction varies as λ−2 whereas the Sunspot extinction changes from about λ−3.5 to about λ−2, suggesting an increasing aerosol component during the day. Water vapor absorption measurements from both sites are similar, though Sunspot shows larger time variations than Haleakala. The instrument-corrected sky brightness from both sites show comparable values, and again the Sunspot data show more variations. The sky brightness values show a radial dependence of sky brightness of r−0.1 at Haleakala, but a dependence of r−1.0 at Sunspot. The wavelength variation of the sky brightness at Haleakala is relatively constant at λ−1.5 but varies at Sunspot from λ−1.5 to λ−0.1 again suggesting an increasing aerosol contribution during the day at Sunspot. Finally, dust measurements near the ground are compared with the extinction wavelength exponent for data taken at Haleakala on 24 Feb. 2003. The measurements suggest more large dust particles are present near the ground than averaged over the whole air column.

Interferometric calorimeter for the measurement of water-vapor absorption

An interferometric calorimeter has been developed to measure the optical-absorption coefficient of gases at the level of 10−10 cm−1. The system operates by measuring the phase shift on a cw He–Ne laser probe beam, which is caused by the expansion of the gas after it has been heated in the focal volume of a pulsed excitation laser beam. The minimum detectable fringe shift is approximately 2 × 10−5 waves. For a 1-J excitation laser this shift corresponds to an absorption coefficient of 2 × 10−10 cm−1. The continuum absorption of water vapor at 9466 cm−1 has been measured to be 6 × 10−10 cm−1 at a 16.5-Torr partial pressure in a 1-atm (760 Torr) N2 buffer at 30°C.

Investigations on bottom sediments of Hungarian rivers and reservoirs: Determination of mineraological compositions by instrumental analytical methods

Bottom sediments taken from Sajó and Tisza Rivers and Kisköre Reservoir were investigated by infrared spectroscopic and thermoanalytical methods. Mineralogical compositions, the amount of organic compounds and minerals were determined. The degree of crystallinity of clay minerals and quartz was examined by selecting two proper infrared absorption ratios. The amount of silicon dioxide, quartz and the specific surface area of the samples were determined by a classical analytical method, X-ray powder diffraction and water vapor absorption measurements, respectively.

Water vapor–nitrogen absorption at CO_2 laser frequencies

In this paper we report the results of a series of pressure-broadened water vapor absorption measurements at 27 CO(2) laser frequencies between 935 cm(-1) and 1082 cm(-1). Both multiple traversal cell and optoacoustic (spectrophone) techniques were utilized together with an electronically stabilized cw CO(2) laser. Comparison of the results obtained by these two methods shows remarkable agreement, indicating a precision which has not been previously achieved in pressure-broadened studies of water vapor. The data of 10.59 microm substantiate the existence of the large (>200) self-broadening coefficients determined in an earlier study by McCoy. In this work we have treated the case of water vapor in N(2) at a total pressure of 1 atm. We have also studied water vapor in air and will report those results separately.

Characterization of the Particle Size and the Crystallinity of Certain Minerals by IR Spectrophotometry and other Instrumental Methods—II. Investigations on Quartz and Feldspar

AbstractInfrared spectra of two minerals; Urkut quartz (Hungary) and a Swedish feldspar, of different origin with different physical characteristics and crystallinity were studied. Samples were taken after appropriate grinding, and infrared spectra, X-ray powder diffraction and water vapor absorption measurements were made along with electronmicrographs. Quantitative conclusions were drawn from changes of particle size and the ratio of bands of the Si—O groups and also the degree of crystallinity and changes of the particle size, respectively.

Water vapor absorption of carbon dioxide laser radiation

An optoacoustic detector or spectrophone has been used to perform detailed measurements of the absorptivity of mixtures of water vapor in air. A C(12) O(2)(16) laser was used as the source, and measurements were made. at forty-nine different wavelengths from 9.2 microm to 10.7 microm. The details of the optoacoustic detector and its calibration are presented, along with a discussion of its performance characteristics. The results of the measurements of water vapor absorption show that the continuum absorption in the wavelength range covered is 5-10% lower than previous measurements.

Optoacoustic measurements of water vapor absorption at selected CO laser wavelengths in the 5-μm region

Measurements of water vapor absorption were taken with a resonant optoacoustical detector (cylindrical pyrex detector, two BaF2 windows fitted into end plates at slight tilt to suppress Fabry-Perot resonances), for lack of confidence in existing spectral tabular data for the 5-7 micron region, as line shapes in the wing regions of water vapor lines are difficult to characterize. The measurements are required for air pollution studies using a CO laser, to find the differential absorption at the wavelengths in question due to atmospheric constituents other than water vapor. The design and performance of the optoacoustical detector are presented. Effects of absorption by ambient NO are considered, and the fixed-frequency discretely tunable CO laser is found suitable for monitoring urban NO concentrations in a fairly dry climate, using the water vapor absorption data obtained in the study.

Study of decationized and dealuminized mordenites by the differential-thermal analysis method and measurement of water vapor absorption

1. The temperature limit for the heat stability of molecular water in a mordenite decreases in measure with the decationization and dealuminization. 2. The dealuminization process is accompanied by a decrease in the number of hydrophilic centers, which role can be played by hydroxyl groups, sodium ions, or dehydroxylated centers that contain the aluminum ion.

Direct Measurement of Water Vapor Absorption of Solar Radiation in the Free Atmosphere

Abstract Aircraft measurements of the vertical profile of net shortwave flux and atmospheric water vapor over the ocean agree with Yamamoto's calculated relation between shortwave absorptivity and water path over the range of water paths 0.01 to 3 cm. The measurements indicate also that some fairly severe form of pressure correction needs to be applied to water path information used in this connection. Data obtained on two very hazy days indicate extra absorption on those days of about 5%.

A high-Q Fabry-Perot interferometer for water vapor absorption measurements in the 100 Gc/s to 300 Gc/s frequency range

The investigation of atmospheric losses in the far-infrared and submillimeter wavelength regions has been pursued from both ends of the spectrum, i.e., from the infrared using IR spectroscopic techniques, and from the microwave region using coherent, high resolution spectroscopic methods. This paper describes the design of a Fabry-Perot semi-confocal interferometer, and its application to the measurement of atmospheric gas losses using coherent sources in the 100 Gc/s to 300 Gc/s frequency range. The tunable interferometer exhibits Q's as large as 3 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> at 300 Gc/s, permitting the measurement of loss with a sensitivity of tan δ= 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-8</sup> and an error of five percent or less.