Optical Constants of Titan Candidate Ices Relevant to Cassini Data: A New Laboratory Set-Up

Details Optical Constants of Titan Candidate Ices Relevant to Cassini Data: A New Laboratory Set-Up Optical Constants of Titan Candidate Ices Relevant to Cassini Data: A New Laboratory Set-Up

Sep 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008dps....40.3121m&link_type=abstract

American Astronomical Society, DPS meeting #40, #31.21; Bulletin of the American Astronomical Society, Vol. 40, p.450

Astronomy and Astrophysics

Astronomy

Scientific paper

Cassini CIRS spectra of Titan's winter pole reveal signatures of a complex array of atmospheric gases and ices in the 8 - 100 micron region. While many of the gas-phase features have been assigned, there are few identifications of solid-phase infrared features as disagreements regarding band positions and shapes exist between Titan spectra and laboratory data. Moreover, most laboratory measurements have been made on pure nitrile ices, and relatively little work has been published on likely Titan ice mixtures at relevant temperatures. From our earlier studies, we recognize that IR band positions of ices can be strongly influenced by sample phase, temperature, and composition. Therefore, we have begun a program to measure spectra and optical constants of ices made of molecules known or suspected to be in Titan's atmosphere and to analyze these ices at different temperatures.
Our new laboratory effort uses a dedicated FTIR spectrometer to record transmission spectra of thin-film ice samples over the 8 - 100 micron region (1250 - 100 cm-1). Laser interference is used to measure film thickness during condensation onto a transparent cold window attached to the tail section of a helium cryostat. Optical constants, real (n) and imaginary (k) refractive indices, are determined using Kramers-Kronig (KK) analysis and/or by modeling absorption with an appropriate number of Lorentzian oscillators. Consistency between calculated transmission determined from a sum of Lorentzian oscillators and iterated KK analysis of the resulting spectrum is demonstrated. Our calculation reproduces the complete spectrum, including all interference effects, so sinusoidal baseline removal is not required. New results produced using KK analysis and comparison with a Lorentz oscillator fit will be discussed along with an update on the state of our ongoing measurements.
Support for this work comes from the NASA's Cassini Data Analysis Program

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