Godfrey T. Sill

Ice clathrate as a possible source of the atmospheres of the terrestrial planets

Abstract The presence and compositions of atmospheres on the terrestrial planets do not follow directly from condensation models which would have Earth accreting near 500°K. No single mechanism yet proposed adequately accounts for the abundances of noble gases and carbon and nitrogen in the atmospheres. We show that the composition of clathrates forming at low temperatures in cold regions of the nebula can be predicted. Addition of about 1 ppm clathrate material to the Earth can explain observed abundances of Ar, Kr, and Xe. Condensation and adsorption processes occuring at 400–500°K are necessary to explain the observed abundances of Ne, H 2 O, C, and N. Possible sources of clathrates could be cometary bodies formed in the outer solar system.

Absorption coefficients of solid NH 3 from 50 to 7000 cm −1

Thin-film spectra of solid NH3 at a resolution of 1 cm−1 were used to determine its absorption coefficient over the range 50–7000 cm−1. The thin films were formed inside a liquid N2 cooled dewar using a variety of substrates and dewar windows. The spectra were recorded with two Fourier spectrometers, one covering the range from 1 to 4 μm and the other from 2.6 to 200 μm. The thickness of the films was measured with a laser interference technique. The absorption coefficients were determined by application of Lambert’s law and by a fitting procedure to the observed spectra using thin-film theory. Good agreement was found with the absorption coefficients recently determined by other investigators over a more restricted wavelength range. A metastable phase was observed near a temperature of 90°K and its absorption coefficient is reported. No other major spectral changes with temperature were noted for the range 88–120°K.

Infrared Intensity Measurements of Cryodeposited Thin Films of NH3, NH4HS, H2S, and Assignments of Absorption Bands:

Interferometric infrared spectral transmission measurements from 60 to 10 000 cm−1 were made for thin films of NH3, NH4HS, and H2S cryodeposits, and recorded as a function of thickness and temperature from 88 K to evaporation points. Integrated band intensities were measured and are reported for all major absorptions. Assignments for lattice and internal fundamental modes are discussed. Particular attention is devoted to the various reported phases of solid NH3, and it is concluded that three phases are supported by experimental evidence: the stable cubic phase, a low temperature amorphous phase, and an intermediate temperature metastable phase. Results and changes of the spectra as a function of temperature will be summarized. Intercomparisons of the spectra obtained for the three cryodeposits are made.

The infrared spectrum of ammonia hydrate: Explanation for a reported ammonia phase

A number of anomalous spectra of solid NH3 deposited from the vapor phase have appeared in the literature. These spectra have been ascribed to a new phase of NH3. In the experiment reported here these anomalous spectra were reproduced by depositing a thin film from a mixture of gaseous NH3 and H2O and annealing this film at a temperature of 162 °K. The thin film spectra showed excellent agreement with recent data on NH3⋅H2O. The anomalous ’’NH3’’ spectra are, therefore, seen to be caused by H2O contamination of solid NH3 with formation of NH3 hydrate.

The clouds of Venus: Sulfuric acid by the lead chamber process☆

Abstract The Pioneer Venus atmospheric probe provided new data on the louds of Venus. A model consistent with this data involves SO 2 being oxidized to H 2 SO 4 by NO x in the presence of H 2 O. NO x also forms nitrosylsulfuric acid (NOHSO 4 ) dissolved in the H 2 SO 4 droplets. This acid solution, along with SO 2 and perhaps NO 2 , can explain the uv and visible reflection spectrum of Venus. In the middle and lower clouds NOHSO 4 forms solid particles.

Geochemical Problems in the Production of the Venus Clouds

Spectroscopic evidence is strong that the clouds of Venus are composed of ferrous chloride hydrate. At the surface of the planet it appears as though the vapor pressure of ferrous chloride may be quite low (10-6 atm), especially if such vapor is allowed to come to equilibrium with the other constituents of the Venus atmosphere. The formation of magnetite (Fe3O4) may be favored, and the spectrum of magnetite is shown in relation to the spectrum of the Venus cloud cover. The presence of ferrous chloride in the upper atmosphere may be due to a non-equilibrium condition.