Emissivity of terrestrial materials in the 3–5 μm atmospheric window☆

Advanced models of fuel droplet heating and evaporation

The previously reported nonreproducibility of the intensity of the OH stretching band of liquid water has been explored. It was found that it can be eliminated in measurements with the Circle® multiple ATR cell by ensuring that the ATR rod is coaxial with the glass liquid holder. It was also found that normal laboratory temperature variations of a few degrees change the intensity by ≤~1% of the peak height. A new imaginary refractive index spectrum of water has been determined between 4000 and 700 cm-1 as the average of spectra calculated from ATR spectra recorded by four workers in our laboratory over the past seven years. It was obtained under experimental and computational conditions superior to those used previously, but is only marginally different from the spectra reported in 1989. In particular, the integrated intensities of the fundamentals are not changed significantly from those reported in 1989. The available imaginary refractive index, k, values between 15,000 and 1 cm-1 have been compared. The values that are judged to be the most reliable have been combined into a recommended k spectrum of H2O(l) at 25°C between 15,000 and 1 cm-1, from which the real refractive index spectrum has been calculated by Kramers-Kronig transformation. The recommended values of the real and imaginary refractive indices and molar absorption coefficients of liquid water at 25 ± 1 °C are presented in graphs and tables. The real and imaginary dielectric constants and the real and imaginary molar polarizabilities in this wavenumber range can be calculated from the tables. Conservatively estimated probable errors of the recommended k values are given. The precision with which the values can be measured in one laboratory and the relative errors between regions are, of course, far smaller than these probable errors. The recommended k values should be of considerable value as interim standard intensities of liquid water, which will facilitate the transfer of intensities between laboratories.

Infrared Intensities of Liquids XX: The Intensity of the OH Stretching Band of Liquid Water Revisited, and the Best Current Values of the Optical Constants of H 2 O(l) at 25°C between 15,000 and 1 cm -1

All the currently available experimental permittivity data for pure water are used to derive an interpolation function that precisely represents e(ν,t,) at standard atmospheric pressure, for frequencies and temperatures in the ranges 0⩽ν⩽25THz and 0⩽t⩽100°C. The permittivity data is represented in terms of relaxations and resonances processes. There are three relaxations in the microwave region and two resonances in the far infrared. The temperature dependence of the relaxation and resonance parameters are determined. For example, at 25°C the three relaxation frequencies are 18.56GHz, 167.83GHz, 1.944THz and the two resonance frequencies are 4.03 and 14.48THz.

Permittivity of pure water, at standard atmospheric pressure, over the frequency range 0-25 THz and the temperature range 0-100 °C

Temperature dependence of the optical constants for liquid H2O and D2O in the far IR region

We have compared the near-normal-incidence spectral reflectance of water at 1, 16, 39, and 50 °C with the corresponding spectral reflectance of water at 27°C, at which temperature the optical constants n(ν) and k(ν) have been previously determined. By applying Kramers-Kronig analyses to the resulting values of spectral reflectance we have obtained the optical constants of water at each of the above temperatures. We present the results in graphical form for the spectral region 400–5000 cm−1 and in tabular form in the vicinity of major absorption and dispersion features. The bearing of our results on the intermolecular structure of water is discussed.

Optical constants of water in the infrared: Influence of temperature*

We have made quantitative measurements of the ratio of the infrared spectral reflectance of standard sea water at near-normal incidence to the corresponding spectral reflectance of pure water at 27°C. The infrared spectral reflectance of standard sea water was determined from the measured ratio and the known optical constants for pure water. The real n(ν) and the imaginary k(ν) parts of the complex index of refraction of standard sea water were then determined by Kramer-Kronig methods. The results obtained for the standard sea water are compared with previous results obtained for pure water and with previous studies of sea water.

Optical properties of sea water in the infrared

Results are presented for measurements of the IR spectral reflectance at near-normal incidence of aqueous solutions of sulfuric acid with acid concentrations of 75% and 95.6% by weight. Kramers-Kronig analyses of the reflectance data are employed to obtain values of the optical constants n(nu) and k(nu) in the spectral range from 400 to 6000 cm to the -1 power. The optical constants of these solutions at 250 K and 300 K are compared. It is found that in spectral regions remote from strong absorption bands, the values of the n(nu) indices obtained at 250 K agree with the values given by Lorentz-Lorenz correction of the same indices at 300 K. All absorption bands observed at 300 K are found to be present at 250 K with slight shifts in frequency and with significant differences in the k(nu) indices at the band maxima. Based on these results, it is concluded that the clouds of Venus probably consist of droplets of aqueous solutions of sulfuric acid with acid concentrations of about 75% by weight.

The infrared optical constants of sulfuric acid at 250 K

The infrared spectral reflectance at near normal incidence has been measured for 3.2 M, 2.4 M, and 1.6 M solutions of ammonium sulfate, an aerosol abundant in the stratosphere and also present in the troposphere. Kramers-Kronig analysis was used to determine values of the refractive and absorption indices from the measured spectral reflectance. A synthetic spectrum of crystalline ammonium sulfate was obtained by extrapolation of the absorption index obtained for the solution to the absorber number densities of the NH4 and SO4 ions characteristic of the crystal.

Optical constants of ammonium sulfate in the infrared

Kramers-Kronig analysis is applied to measured values of spectral reflectance at near-normal incidence to determine the real and the imaginary parts of the complex index of refraction for methane, ethane, propane, n-butane, n-hexane, n-heptane, and n-decane in the liquid state. The results indicate that the strengths of the characteristic bands as measured by the integral of the imaginary part are roughly constant for all the liquid alkanes except for methane. The intensity of the CH valence vibration bands in the spectra of the alkanes except methane is directly proportional to the number of CH groups per unit volume. The relations for the intensity of the bands due to CH2 and CH3 deformations are examined. Characteristic band intensities of the type established for NH4(+) and SO4(2-) groups in solutions and crystals cannot be extended to the more closely coupled CH2 and CH3 groups in alkane molecules.

Lary W. Pinkley

Papers

Optical constants of water in the infrared: Influence of temperature*

Optical properties of sea water in the infrared

The infrared optical constants of sulfuric acid at 250 K

Optical constants of ammonium sulfate in the infrared

Infrared band intensities of saturated hydrocarbons