Publications (10)6.77 Total impact
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Article: Discovery of a second narrow absorption feature in the near-infrared spectrum of Io
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ABSTRACT: A high resolution survey of the near-IR reflectance spectrum of Io has shown a sharp absorption feature centered at 5045 +/- 1/cm; this feature is not present in laboratory spectra of dilute CO2 in a matrix. Since the spectrum of cold H2S ice crystals exhibits structure near this wavelength, it is suggested that either (1) the difference in width between this feature and that of the much broader Ionian H2S ice may be due to the presence of different phases of ice at different temperatures, so that these are emphasized in the different spectral regions, or (2) H2S is trapped in an SO2 matrix.08/1992; -
Article: KPNO 4m FTS Observations of the Infrared Band at 2.125 μm (4705 cm-1) in the Spectrum of Io
05/1991; 23:1231. -
Article: Another Unidentified Near-IR Absorption Feature on Io
05/1991; 23:1230. -
Article: Mutual Event Observations of Io's 2.125 μm (4705 cm-1) Absorption Feature: The Latitudinal Distribution of the Source Material
05/1991; 23:1228. -
Article: A new class of absorption feature in Io's near-infrared spectrum.
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ABSTRACT: We report our discovery of an absorption feature in the infrared spectrum of Io centered at 2.1253 micrometers (4705.2 cm-1). This band is marginally resolved at resolving power 1200 with a deconvolved full width at half-maximum (FWHM) of about 4 cm-1. This contrasts with the 30- to 50-cm-1 widths of the broad absorption features previously detected at longer wavelengths which arise from mixtures of SO2 with H2S and H2O. This newly discovered feature is relatively weak, having a core only 5% below the continuum at this resolving power. Our survey from 1.98 to 2.46 micrometers (5050-4065 cm-1) at this same resolving power revealed no other feature greater than 1% of the continuum level shortward of 2.35 micrometers, and 3% elsewhere. The feature does not correspond to any gas- or solid-phase absorption that might be expected from previously identified constituents of Io's surface. No temporal or longitudinal variation has been detected in the course of 18 nights of observation over the past year and no significant variation in the strength of the feature was seen during an emergence from eclipse. These observations indicate that the source material of the feature is reasonably stable, and is more uniformly distributed in longitude than Io's hot spots. These characteristics all indicate that the feature belongs to a class different from those characterizing other known absorption features in Io's spectrum. Consequently, it should reveal important new information about Io's atmosphere-surface composition and interaction. A series of laboratory experiments of plausible surface ices indicates that (i) the band does not arise from overtones or combinations of any of the molecular vibrations associated with species already identified on Io (SO2, H2S, H2O) or from chemical complexes of these molecules, (ii) the band does not arise from H2 trapped in SO2, and (iii) the band may arise from the 2 nu3 mode of CO2. If the band arises from CO2, it is clear from its detailed shape and position that the molecules are not embedded in an SO2 matrix, as are H2S and H2O, but may be present as multimers or "clusters."Icarus 02/1991; 89:264-76. · 3.38 Impact Factor -
Article: Laboratory studies of the newly discovered infrared band at 4705.2 cm-1 (2.1253 micrometers) in the spectrum of Io: the tentative identification of CO2.
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ABSTRACT: We discuss over 120 laboratory experiments pertaining to the identification of the new absorption band discovered by Trafton et al. (1991) at 4705.2 cm-1 (2.1253 micrometers) in the spectrum of Io. It is shown that this band is not due to overtones or combinations of the fundamental bands associated with the molecules (or their chemical complexes) already identified on Io, namely, SO2, H2S, and H2O. Thus, this band is due to a new, previously unidentified, component of Io. Experiments also demonstrate that the band is not due to molecular H2 frozen in SO2 frosts. Since the frequency of this band is very close to the first overtone of the nu 3 asymmetric stretching mode of CO2, we have investigated the spectral behavior of CO2 under a variety of conditions appropriate for Io. The profile of the Io band is not consistent with the rotational envelope expected for single, freely rotating, gaseous CO2 under Io-like conditions. It was found that pure, solid CO2 and CO2 intimately mixed in a matrix of solid SO2 and H2S produce bands with similar widths (5-10 cm-1), but that these bands consistently fall at frequencies about 10-20 cm-1 (approximately 0.007 micrometer) lower than the Io band. CO2 in SO2 : H2S ices also produces several additional bands that are not in the Io spectra. The spectral fit improves, however, as the CO2 concentration in SO2 increases, suggesting that CO2-CO2 interactions might be involved. A series of Ar : CO2 and Kr : CO2 matrix isolation experiments, as well as laboratory work done elsewhere, show that CO2 clustering shifts the band position to higher frequencies and provides a better fit to the Io band. Various laboratory experiments have shown that gaseous CO2 molecules have a propensity to cluster between 80 and 100 K, temperatures similar to those found on the colder regions of Io. We thus tentatively identify the newly discovered Io band at 4705.2 cm-1 (2.1253 micrometers) with CO2 multimers or "clusters" on Io. Whether these clusters are buried within an SO2 frost, reside on the surface, or are in a residual, steady-state "atmospheric aerosol" population over local coldtraps is not entirely clear, although we presently favor the latter possibility. The size of these clusters is not well defined, but evidence suggests groups of more than four molecules are required. The absorption strength of the 2 nu 3 CO2 cluster overtone determined in the laboratory, in conjunction with the observed strength of the Io band, suggests that the disk-integrated abundance of CO2 is less than 1% that of the SO2. Studies of the sublimation behavior of CO2 indicate that it probably resides predominantly in the cooler areas (< 100 K) of Io. The relative constancy of the Io feature over a variety of orbital phases suggests that the polar regions may contain much of the material. Some consequences of the physical properties of CO2 under conditions pertinent to Io are discussed. The presence of CO2 clusters on Io could be verified by the detection of any one of several other infrared bands associated with the CO2 molecule, of which the strongest are the nu 3 12CO2 asymmetric stretch fundamental near 2350 cm-1 (4.25 micrometers) and the nu 2 bending mode fundamental near 660 cm-1 (15.1 micrometers). Weaker bands that may also be detectable include the nu 3 13CO2 asymmetric stretch fundamental near 2280 cm-1 (4.39 micrometers), the 2 nu 2 + nu 3 combination/overtone band near 3600 cm-1 (2.78 micrometers), and the nu 1 + nu 3 combination band near 3705 cm-1 (2.70 micrometers).Icarus 01/1991; 91:125-44. · 3.38 Impact Factor -
Article: Laboratory Studies of the Newly Discovered Infrared Band at 4705.2 cm-1 (2.1253 μm) in the Spectrum of Io
05/1990; 22:1110. -
Article: Spatial Distribution of Jupiter's 2-μm Aurorae
05/1989; 21:941. -
Article: Discovery of a second narrow absorption feature in the near-infrared spectrum of Io
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ABSTRACT: Extension of our high resolution survey of the near-infrared reflectance spectrum of Io to shorter wavelengths has revealed a second relatively sharp absorption feature that, in strength, width, and constancy, appears similar to the one discovered in 1990. The new feature is centered at vacuum wavelength 1.9820 ± 0.0005 μm (5045 ± 1 cm−1) and has an equivalent width of about 0.5 cm−1 (5% deep in our spectra). This new feature is not present in the laboratory spectra of dilute CO2 in a matrix, and therefore CO clusters, which have been proposed as an identification for the carrier of the original narrow absorption feature at 2.125 μm, do not appear to be responsible for the second feature. The spectrum of cold H2S ice crystals shows considerable structure near this wavelength. The difference in width between this feature and that of the much broader Ionian H2S ice features at longer wavelengths may be the result of different phases of ice, at different temperatures, that are emphasized in the different spectral regions. Alternatively, the trapping of H2S in an SO2 matrix may account for the small discrepancy in observed wavelength. Possible tests for the H2S identification of the carrier are discussed.Icarus. -
Article: A new class of absorption feature in lo's near-infrared spectrum
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ABSTRACT: We report our discovery of an absorption feature in the infrared spectrum of Io centered at 2.1253 μm (4705.2 cm−2). This contrasts with the 30- to 50-cm−1 widths of the board absorption features previously detected at longer wavelengths which arise from mixtures of SO2 with H2S and H2O. This newly discovered feature is relatively weak, having a core only 5% below the continuum at this resolving power. Our survey from 1.98 to 2.46 μm (5050-4065 cm−1) at this same resolving power revealed no other feature greater than 1% of the continuum level shortward of 2.35 μm, and 3% elsewhere. The feature does not correspond to any gas-or solid-phase absorption that might be expected from previously identified constituents of Io's surface. No temporal of longitudinal variational has been detected in the course of 18 nights of observation over the past year and no significant variation in the strength of the feature was seen during an emergence from eclipse. These observations indicate that the source material of the feature is reasonably stable, and is more uniformly distibuted in longitude than Io's hot spots. These characteristics all indicate that the feature belongs to a class different from those characterizing other known absorption feature in Io's spectrum. Consequently, it should reveal important new information about Io's atmosphere-surface composition and interation. A series of laboratory experiments of plausible surface ices indicates that (i) the band does not arise from overtones or combinations of any of the molecular variations associated with species already identified on Io (SO2, H2S, H2O) or from chemical complexes of these molecules, (ii) the band does not arise from H2 trapped in SO2, and (iii) the band may arise from the 2v3modeofCO2. If the band arises from CO2, it is clear from its detailed shape and position that the molecdules are not embedded in an SO2 matrix, as are H2S and H2O, but may be present as multimers or “clusters.”Icarus.
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- Icarus (2)
Institutions
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1991
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University of Texas at Austin
Port Aransas, TX, USA
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