James R. Aronson

Spectral Reflectance and Emittance of Particulate Materials. 2: Application and Results

Experimental data on the spectral emittance of particulate minerals, obtained using a Michelson interferometer operating between 300 cm(-1) and 1400 cm(-1) are compared with the results of a new theory of the spectral reflectance (emittance) of such materials. The comparisons show that the theory predicts the infrared spectra of minerals quite well both for single substances and mixtures, over the wide particle size range between 0.3 micro and 330 micro. The good agreement suggests that the theory can be used in the application of remote infrared spectroscopy to such problems as the compositional analysis of the surface of a planet.

Infrared spectra from fine particulate surfaces.

Characteristic spectral information can be obtained from a surface composed of fine particles either if the spectrum is observed at sufficiently high signal-to-noise ratio or if the particles are well compacted.

Optical constants of minerals and rocks

Lorentz line parameters (and estimates of their standard deviations) have been empirically derived from measured reflectance data for muscovite mica, an anorthosite, a diopsidic pyroxenite, an almandite-pyrope garnet, and a soda lime glass. These parameters provide a useful starting point for computer calculations requiring optical constants as a function of frequency and are therefore given here. A novel method of fitting the reflectance data by least squares is described in detail, as is the statistical procedure for estimating the standard deviations of the parameters found.

The vibrational spectra of methyltrichlorogermane

Abstract The infrared and Raman spectra of methyltrichlorogermane have been recorded and the eleven active fundamental vibrations of this C3ν molecule are assigned. The frequency of the inactive torsional vibration, ν6, is estimated to be 134 cm−1 from the first overtone band. The height of the barrier hindering internal rotation was calculated to have a value of 1300 cal/mole.

Optical constants of monoclinic anisotropic crystals: gypsum

The principal complex refractive indices for gypsum have been derived in the infrared region of the spectrum. These values were obtained by dispersion analysis of the reflection spectra for E ‖ b and the a-c (monoclinic) plane. Two sets of complex indices are obtained for the latter plane, taking account of axis wander. The oscillator parameters are presented here, together with formulas for calculating the optical constants at any desired infrared frequency. In addition the usefulness of such optical constants for modeling the infrared properties of powders is demonstrated for gypsum and spodumene.

Tunable Diode Laser High Resolution Spectroscopic Measurements of the ν 2 Vibration of Carbon Dioxide

A tunable diode laser spectrometer was used for high resolution measurements on the Q-branch of the nu(2) vibration of carbon dioxide. The infrared source was a current tuned Pb(0.936)Sn(0.064)Se diode laser. A 1-m gas cell was designed to allow variation of temperature (200-300 K) at 1-50 torr of 320 ppm mixtures in nitrogen. Owing to the narrow linewidth of the diode laser, true line shapes may now be measured well into the Doppler region. Line shapes and intensities of several rotational lines (J </= 34) have been measured as a function of pressure and temperature. Initial measurements tend to confirm the theoretical predictions of Drayson as to relative line positions, but show linewidths higher than predicted by Yamamoto et al. The line strengths, at low temperatures, appear to be about 12% greater than those predicted by Drayson.

Infrared emittance of fibrous materials

A theory of the IR emittance of fibrous materials has been developed. The theory predicts the IR spectral emittance of a matte of randomly arrayed cylindrical fibers as a function of the optical constants of the fiber material, the fiber diameter, the packing density of the fibers, the packing of the fibers within fiber bundles, the reflectance of the substrate, and the thickness of the fabric layer. Theoretical simulations were made and compared with experimental measurements of the IR emittance of polypropylene samples. Both the theory and the experimental data confirm the validity of the concept that fabrics can be tailored by a proper choice of the above parameters so as to obtain an emittance distinctly different from unity.

Optical constants of monoclinic anisotropic crystals: Orthoclase

Abstract The optical constants of the monoclinic crystal orthoclase [ideal composition 4(KAlSi 3 O 8 )] have been derived in the i.r. region of the spectrum by the use of dispersion theory. Values for the E || b orientation and for the a — c plane have been used, together with a theory of the emittance of particulate materials, to simulate the spectrum of orthoclase powder.

Effective optical constants of anisotropic materials

The applicability of a technique for determining the optical constants of soil or aerosol components on the basis of measurements of the reflectance or transmittance of inhomogeneous samples of component material is investigated. Optical constants for a sample of very pure quartzite were obtained by a specular reflection technique and line parameters were calculated by classical dispersion theory. Predictions of the reflectance of powdered quartz were then derived from optical constants measured for the anisotropic quartz and for pure quartz crystals, and compared with experimental measurements. The calculated spectra are found to resemble each other moderately well in shape, however the reflectance level calculated from the psuedo-optical constants (quartzite) is consistently below that calculated from quartz values. The spectrum calculated from the quartz optical constants is also shown to represent the experimental nonrestrahlen features more accurately. It is thus concluded that although optical constants derived from inhomogeneous materials may represent the spectral features of a powdered sample qualitatively a quantitative fit to observed data is not likely.

Optical constants of triclinic anisotropic crystals: blue vitriol

The principal complex refractive indices for blue vitriol (chalcanthite) have been derived in the infrared region of the spectrum. These values were obtained by dispersion analysis of the reflection spectra of a cube of chalcanthite taken with the electric vector at three orthogonal orientations involving two orthogonal arbitrarily oriented faces. This derivation of the optical constants in terms of the dispersion parameters, taking account of axis wander, demonstrates that it is now possible for any crystalline substance to be analyzed regardless of crystal system.