Title Spectroscopic effects in CH4/H2O ices
Author Gálvez, O.; Maté, B.; Herrero, V.J.; Escribano, R.
Author Affil Gálvez, O., CSIC, Instituto de Estructura de la Materia, Madrid, Spain
Source The Astrophysical Journal, 703(2), p.2101-2107, . Publisher: University of Chicago Press for the American Astronomical Society, Chicago, IL, United States. ISSN: 0004-637X
Publication Date Oct. 1, 2009
Notes In English. 33 refs. GeoRef Acc. No: 310091
Index Terms experimentation; hydrocarbons; ice; infrared spectroscopy; spectra; spectroscopy; temperature; water; water temperature; aliphatic hydrocarbons; alkanes; experimental studies; infrared spectra; Kuiper Belt; laboratory studies; methane; organic compounds; solar system; stoichiometry
Abstract Recent observations of CH4 in different astrophysical objects encourage laboratory research on methane/water ice mixtures. An IR spectroscopy laboratory investigation is presented on these systems. Co-deposited samples are formed by vapor deposition of CH4 and H2O on a cold substrate, in a wide range of stoichiometries, from very diluted mixtures to CH4/H2O=2.5 values. Samples are prepared at 14 K and at 40 K, and their temperature behavior is studied when they are warmed up to 60 K. The spectroscopic analysis is centered on the methane features, and also on the water dangling bonds (DBs) that appear in the spectra of the mixtures. The IR forbidden nu 1 band shows up in the spectrum (3.44 µm), indicating some form of distorted methane. The combination bands nu 3+nu 4 and nu 1+nu 4 are seen at 2.32 and 2.38 µm, and the nu 2+nu 3 band weakly at 2.21 µm. Whereas nu 3 is not shifted in spectra of mixed samples, the wavenumber peak of nu 4 and its combination bands vary in a 6 cm-1 range, providing a possible estimation for the relative methane concentration in the sample. Bands in the spectra of mixtures are always broader than their counterparts in pure CH4 ice. The intensity of nu 4 appears to increase in mixed samples with respect to the pure solid. Raising the temperature of the ices up to 60 K liberates part of the methane, but a fraction is retained with a maximum value of ~7% ±2%. This limit may provide information on the temperature properties of astrophysical objects. The different spectral characteristics of water DBs with increasing methane proportion in mixed samples can also furnish information to estimate the stoichiometry of the mixture. Copyright (Copyright) 2009. The American Astronomical Society. All rights reserved.
URL http://hdl.handle.net/10.1088/0004-637X/703/2/2101
Publication Type journal article
Record ID 65006762