Peter M. Silvaggio

The surface and atmosphere of Pluto

Abstract A new spectrum of Pluto in the region 1.4 to 1.9 μm provides confirmation of the presence of solid methane on the planets surface. Considerations of vapor pressure of methane gas above the solid indicate the presence of a tenuous atmosphere of this gas, the surface partial pressure of which is variable from perihelion to aphelion. The implication of a high surface albedo, the newly derived mass of Pluto, and inferences as to the range of plausible bulk mean densities, indicate that the radius of Pluto should lie in the range 1200 to 1800 km.

Temperature dependence of intensities of the 8–12 μm bands of CFCl3

Abstract The absolute intensities of the 8–12 μm bands from freon 11 (CFCl 3 ) were measured at temperatures of 294 and 216°K. Intensities of the bands centered at 798, 847, 934, and 1082 cm -1 are all observed to depend on temperature. The temperature dependence for the 847 and 1082 cm -1 fundamental regions is attributed to underlying hot bands; for the ν 2 + ν 5 combination band (934 cm -1 ), the observed temperature dependence is in close agreement with theoretical prediction. The implication of these results on atmospheric i.r. remote-sensing is briefly discussed.

First Results from the Large Probe Infrared Radiometer Experiment

During the descent to the surface of Venus, the large probe infrared radiometer measured the net thermal radiative flux in several spectral bandpasses. Preliminary analysis has permitted us to estimate (i) the infrared extinction coefficient profile attributable to aerosols, with respect to their visible profile, in the upper atmosphere of Venus and (ii) the water vapor mixing ratio below the clouds. An indication of the composition of a multicomponent cloud is seen in the data from the spectral bandpass from 6 to 7 micrometers.

Investigation of the 2-0 pressure-induced vibrational absorption spectrum of hydrogen at temperatures below ambient

Abstract A theoretical fit has been made to oue laboratory measurements of the 2-0 collisionally induced H2 absorption band for temperatures of 122 and 273.3 K and at a density of 20 amagats. A Lennard-Jones 6–12 intermolecular potential and a Birnbaum-Cohen line profile have been used. The fit resulted in a chi-square of 0.2%. Line widths have also been derived as a function of temperature. The lifetimes of the states have been calculated.

Band model calculations for CFCl3 in the 8–12 μm region

Abstract A Goody random band model with a Voigt line profile is used to calculate the band absorption of CFCl 3 at various pressures at room and statospheric (216°K) temperatures. Absorption coefficients and line spacings are computed.

Band model analysis of the H2O2 ν6(b) band

A Mayer-Goody random band model with a Voigt line profile is used to derive interval absorption coefficients, mean line spacings, and pressure-broadening coefficients for the ν6(b) H2O2 band centered at 1265 cm−1 at 285°K.

Intensity of the sulfur dioxide rotational spectrum

Abstract The integral band intensity of the pure rotational absorption of SO2 gas has been determined from far-i.r. spectra. From the curve of growth, the value at 298°K is found to be Sob = 35.2±1.5atm-1 -cm-2. The entire set of experimental data has been analyzed using an absorption band model. The derived intensity agrees with that obtained from the curve of growth to be better than 10%. This result should be of value in connection with atmospheric models of the planet Venus.

The use of intermolecular potential functions in fitting pressure induced spectra

Abstract It is important to use physically realistic derivatives of the intermolecular potential when fitting pressure-induced spectra; otherwise, second-order temperature effects may be masked. Examples are presented.