Water Vapor Spectrum Research Articles

A compact Sun tracking radiometer with two different beamwidth antennas for detection of atmospheric water vapor

A compact radiometer system having two small antennas of different beamwidths was developed to detect water vapor concentration by measuring atmospheric attenuations of the solar radiation at the K-band. To obtain continuous monitoring of the total water-vapor fluctuation, a simplified measuring method was used, which was a cancellation of the thermal radiation of the atmosphere by measuring the temperature difference of the two antennas fluctuation by taking the ratio of measured data at two frequency points in the water-vapor absorption spectrum. Errors in the estimation of total water vapor arising from the simplified method were evaluated. Experimental results have shown general agreement in the trend of theoretically calculated results against absolute humidity at ground level, and hence, total water-vapor content or integrated water vapor, when the standard atmospheric altitude distribution of water vapor is assumed. >

On the nature of the infrared spectrum of water vapor between 8 and 14 μm

Some new results on the continuum absorption of water vapor in the thermal i.r. between 8 and 14μm are presented along with a brief review of currently adapted empirical and semi-empirical models explaining its nature. The original suggestion by Penner1 that the observed absorption might be by dimers of water molecules in the vapor phase is reexamined in light of the new results.

Foreign-gas collision broadening of the far-infrared spectrum of water vapor

The far-infrared rotational spectrum of H2(O-16) has been studied in the spectral range 25-112/cm to measure the foreign-gas collision-broadened linewidths. Measurements of 17 lines broadened by nitrogen and 21 lines broadened by oxygen are reported. The measurements were made at 297 K. From these data, the widths due to air broadening are obtained. The experimental results are compared with recent theoretical calculations and with the case of a constant linewidth, equal to the average experimental width. There is some correlation between the relative experimental linewidths and the theoretical predictions. However, the simple assumption of a constant value for the collision-broadened linewidths gives a better representation for the case of N2- and O2-broadened linewidths than do present detailed theoretical calculations.

Self- and N 2-broadened spectra of water vapor between 7.5 and 14.5 μm

Self- and N 2-broadened absorption spectra of water vapor have been measured in the infrared between 7.5 and 14.5 μm at 294, 311, 333 and 339 K. The so-called continuum aspect of the observed absorption coefficients is interpreted in terms of existing theoretical models.

Rotational spectrum of the H 216O molecule in the (010) excited vibrational state

Five new MW lines of the pure rotational spectrum of water vapor in the (010) excited state have been measured. The analysis of the available data on the (010) vibrational state has been carried out using either a conventional model or a one-dimensional Borel approximation of a Watson-type Hamiltonian. In both cases a model with 24 parameters up to J 8 was used. The use of the Borel-approximated Watson Hamiltonian resulted in a fit of the experimental data within experimental uncertainty, whereas the fit using the conventional model produced a standard deviation 60 times worse.

H218O: line positions and intensities between 9500 and 11 500 cm−1. The (041), (220), (121), (300), (201), (102), and (003) interacting states

The spectrum of 18O-enriched water vapor has been recorded between 9500 and 11 500 cm−1, with the aid of a Fourier-transform spectrometer. Its analysis has allowed the determination of 419 accurate rotational energy levels belonging to seven interacting vibrational states of H218O: (041), (220), (121), (300), (201), (102), and (003). Moreover, 622 line intensities belonging to the 4ν2 + ν3, 2ν1 + 2ν2, ν1 + 2ν2 + ν3, 3ν1, 2ν1 + ν3, ν1 + 2ν3, and 3ν3 bands have been measured with an average uncertainty of 6%.

Stieltjes imaging method for molecular Auger transition rates: Application to the Auger spectrum of water.

A Stieltjes imaging method for the calculation of molecular Auger transition rates within Wentzel's ansatz is devised and numerically applied to the Auger emission spectrum of water vapor. Continuum orbitals are solved in the anisotropic field of the doubly ionized molecule using an extended set of ${L}^{2}$ integrable basis functions. The effects on the Auger rates of nonorthogonality between the bound orbitals (electronic relaxation) as well as of hole mixing due to the interaction of the residual final states are numerically evaluated and discussed. Comparisons are made with a previously devised atomic decomposition scheme and with experiment. The summation of Auger channel rates gives a value of 0.15 eV for the lifetime broadening of the core-hole state of water.

A new treatment of water vapor opacity

Although the bands of H2O are strong in cool stars, water vapor opacity has generally not been accurately treated due both to the inadequacy of laboratory data and the difficulty of treating the millions of lines involved. We report a new treatment based upon a statistical representation of the water vapor spectrum derived from available laboratory data. The statistical spectrum of water follows an exponential distribution of line strengths and random positions of lines to reproduce the line spacings and mean opacities observed in the laboratory. This statistical spectrum is then randomly sampled in the spirit of opacity sampling. Significant improvements are made in both the opacities and in the thermal structure and emergent fluxes of the model atmospheres.

Horizontal spectra of atmospheric tracers measured during the Global Atmospheric Sampling Program

Variance power spectra of potential temperature, ozone, carbon monoxide, and water vapor at airliner cruise altitudes are presented. These results are based on data collected aboard commercial airlines at cruise altitudes during the Global Atmospheric Sampling Program (GASP). The horizontal scales (wavelengths) resolved by these data extend from 2.6–2400 km for temperature, 10–2400 km for ozone, 150–3000 km for water vapor, and 300–2500 km for carbon monoxide. The results divide into two distinct regimes in most cases, with the transition found at 500‐ to 800‐km wavelength. The long wavelength regime of temperature behaves as predicted by geostrophic turbulence theory, but only some of the chemical tracer results fit this model. At scales less than 500–800 km, spectral shapes of all tracers follow an approximately −5/3 power law dependence on wave number. At scales less than about 100 km, tropospheric ozone spectra follow a −1 power law. Spectral amplitudes of potential temperature and ozone are larger in the stratosphere than in the troposphere, while spectral amplitudes of carbon monoxide and water vapor are larger in the troposphere. The horizontal fluctuations giving rise to these spectra apparently result from that component of a spectrum of quasi‐horizontal displacements which acts orthogonal to the background gradient of each tracer. Numerical checks support this hypothesis for each of the chemical tracers, assuming the tracers are horizontally stratified. Finally, it is found that the frequency distribution of ozone spectral magnitude at a given wave number is approximately lognormal.

The first hexad {(040), (120), (021), (200), (101), (002)} of H218O: experimental energy levels and line intensities

The spectrum of 18O-enriched water vapor has been recorded between 5900 and 8000 cm−1, with the aid of a Fourier-transform spectrometer. Its analysis allowed the determination of 437 accurate rotational levels belonging to the hexad of interacting states {(040), (120), (021), (200), (101), (002)}of H218O. Among these vibrational states, the (040), (120), and (002) ones had never been observed before. Moreover, 726 line intensities belonging to the 4ν2, ν1 + 2ν2, 2ν2 + ν3, 2ν1, ν1 + ν3, and 2ν3 bands have been measured with an uncertainty of 6%.

Infrared absorption by gas mixtures in the 500—700 K temperature range II— 2.7 μm H 2O spectra

The absorption spectra of water vapor in the 2.7 μm-band have been obtaine in an isothermal, vacuum-tight cell with a resolution of 0.8 cm -1. They are compared with a line-by-line calculation using AFGL data and the approximate temperature-dependence of the line-widths. Agreement is very satisfactory in some spectral regions and rather poor in others.

The high-resolution spectrum of water vapor between 13 200 and 16 500 cm −1

High-resolution Fourier transform spectra of water vapor between 13 200 and 16 500 cm −1 have been analyzed, leading to a precise and extensive set of line positions, line intensities, and rotational energy levels of highly excited vibrational states.

IR-spectroscopy of the atmosphere

The infrared technique of measuring trace gases in the air has been evolving for many years, with rapid progress during the last ten years. Air pollution research requires such measurements for mixing ratios as low as 10−10. This calls for long optical paths, such as the path from a high altitude observing point to a setting sun. At ground level the best way to achieve a long enough path is to use J.U. White's 3-mirror multiple-pass cell. The infrared method has had its greatest success in the study of the upper atmosphere using balloon-borne spectrometers aimed at the sun. Measurements through the upper atmosphere do not have significant interference from water vapor. At ground level, however, the water vapor absorbs nearly everywhere in the spectrum, and it is necessary to detect the trace gases by the small perturbations they make on the water vapor spectrum. The Fourier transform (FT) spectrometer has been responsible for recent progress. For studies in the lower atmosphere one can obtain superb spectra by combining an FT instrument of about 0.1 cm−1 resolution with a White cell made from mirrors of modest size. Nitrogen-cooled detectors should be used. The path may be in the open air. With an FT instrument, signal fluctuations caused by air turbulence do not appear to introduce noise into the spectrum. This is a result of the multiplexing and the high frequency modulation. Pollutants that have been measured by infrared in ambient air have included HNO3, HNO2, NH3, O3, CO, CO2, SO2, NO, NO2, H2CO, HCOOH, hydrocarbons, peroxy nitrates, HCl and HF. Further study should extend this list.

Turbulence spectra of CO2, water vapor, temperature and wind velocity fluctuations over a crop surface

A prototype rapid-response CO2 sensor was used in conjunction with a Lyman-alpha hygrometer, fine-wire thermocouples and a three-dimensional drag anemometer to measure CO2, humidity, temperature and wind velocity fluctuations. Measurements were made over a soybean crop grown on relatively flat terrain near Mead, Nebraska.

The high-resolution spectrum of water vapor between 16500 and 25250 cm −1

High-resolution spectra of water vapor have been recorded, with very good signal-to-noise ratios, between 16500 and 25250 cm −1 using visible Fourier transform spectroscopy. Precise line positions have been derived, and 1174 vibration-rotation transitions belonging to 23 different bands of H 2O have been assigned, leading to the determination of 539 vibration-rotation energy levels and greatly extending our knowledge of the highly excited vibrational states of the water molecule. The measurement of 630 line intensities with accuracies varying from 5 to 35%, depending on the strength of the line, has been performed.

H218O: The (030), (110), and (011) interacting states. Line positions and intensities for the 3ν2, ν1 + ν2, and ν2 + ν3 bands

The spectrum of oxygen-18 enriched water vapor was recorded between 4400 and 6100 cm−1 with the aid of a Fourier transform spectrometer. Its analysis allowed the determination of 60 energy levels of the (030) vibrational state of H218O and improvements in the knowledge of the energy levels belonging to the (110) and (011) vibrational states of this molecule. A fit of 330 rotational levels of the (030), (110), and (011) states was performed using 54 effective constants and taking into account the Coriolis-type and Fermi-type interactions. Moreover, 853 line intensities belonging to the 3ν2, ν1 + ν2, and ν2 + ν3 bands were measured. The constants involved in the rotational expansion of the transformed transition moment operator corresponding to these bands were determined through a fit of these line intensities. The constants obtained were then used to compute the whole spectrum of the 3ν2, ν1 + ν2, and ν2 + ν3 bands of H218O. This spectrum should be of interest for atmospheric studies.

Radiative decay of multiply excited core hole states in H2O

A high resolution x-ray emission spectrum of water vapor has been recorded, using a 7 keV electron beam and a 10 m grazing incidence spectrometer. The spectrum is interpreted in terms of dipole transition moments between CI wave functions built from separately optimized molecular orbitals. The principal features of the spectrum are reproduced considering transitions in the singly and doubly ionized species, giving rise to main lines and Wentzel–Druyvesteyn satellites, respectively.

An fir cooled grating spectrometer for the kuiper airborne observatory

The design and performance of a liquid-He-cooled spectrometer being developed for the Kuiper Airborne Observatory (KAO) to study FIR lines originating in the interstellar medium are discussed. Currently, the spectrometer contains six Ge:Ga photoconductor detectors mounted in integrating cavities and cooled to about 3 K; the collimator focal plane has space for 39 such detectors. The instrument achieves a maximum resolving power of 6000 by means of a 45-cm long echelle grating and is optically capable of operating in the spectral range 25-300 microns. A laboratory spectrum of water vapor, an atmospheric water absorption feature measured from the KAO with Mars as a source, and the forbidden O(2+) emission from W51-IRS1 are shown.

Photoacoustic absorption spectra of atmospheric gases near 7603 cm^−1

Absorption spectra of carbon monoxide, water vapor, memane, and ammonia are presented as part of an effort to determine absolute absorption cross sections for some atmospheric gases at the iodine laser wavelength.

Application of the rotational diffusion model to the CARS spectra of high‐temperature, high‐pressure water vapour

AbstractCARS spectra of water vapour at elevated pressures (1–16 bar) and temperatures (300–800 K) have been investigated experimentally and theoretically. A theoretical model of the CARS spectrum of water vapour based on Gordon's rotational diffusion model was tested. The model was adapted to include the effects of vibrational relaxation and dephasing processes. Good agreement was found between experiment and theory for all conditions investigated. Rotational inelastic collisions are dominant and contribute approximately 65% to the overall individual molecular linewidths. As part of the data analysis a new measurement of dσ/dω (H2O)=1.10 × 10−34 ± 20% m2 sr−1 has been made.