Laboratory infrared reflection spectrum of carbon dioxide clathrate hydrates for astrophysical remote sensing applications

Research areas:
Year:
2012
Authors:
Journal:
ICARUS
Volume:
221
Number:
2
Pages:
900-910
Month:
NOV-DEC
ISSN:
0019-1035
Abstract:
We present 1-5 mu m IR reflectance spectra of CO2 clathrate hydrates
acquired under temperature and pressure conditions representative of the
icy moons' surfaces. The IR reflectance spectrum of the CO2 clathrate
hydrates is similar to the water ice IR reflectance spectrum except for
two main absorption bands corresponding to the CO2 guest molecule at
2.71 and 4.28 mu m (3693 and 2334 cm(-1)). The specific configuration of
the clathrate hydrate structure is identified through the nu(3)
absorption band splitting which produces a band at 4.26 mu m (2347
cm(-1)) for molecules trapped in small cages and a band at 4.28 mu m
(2334 cm(-1)) for molecules trapped in large cages. In general, the
reflection spectra are similar to spectra obtained in transmission
spectroscopy. But, it appears that the aspect of the nu(3) absorption
band is strongly influenced by physical (roughness, thickness, mixing
properties) and optical (n and k) characteristics of the sample. A
qualitative discussion of the effects of these sample properties on
near-IR signatures of clathrate hydrates is proposed. Finally, a
comparison between the absorption bands of CO2 clathrate hydrates
obtained in this work and CO2 absorption bands as detected by VIMS on
the icy satellites of Saturn is achieved. The experimental near-IR
reflection spectra, made in pressure-temperature (P-T conditions close
to those of the icy surfaces, confirm that VIMS data are not consistent
with the presence of structure I CO2 clathrate hydrates on the surface
of the icy moons. (C) 2012 Elsevier Inc. All rights reserved.