J/A+A/652/A126 Spectroscopy of CH3OH in layered and mixed ices (Mueller+, 2021)
Spectroscopic measurements of CH3OH in layered and mixed interstellar ice
analogues.
Mueller B., Giuliano B. M., Goto M., Caselli P.
<Astron. Astrophys. 652, A126 (2021)>
=2021A&A...652A.126M 2021A&A...652A.126M (SIMBAD/NED BibCode)
ADC_Keywords: Spectra, infrared ; Spectroscopy
Keywords: astrochemistry - methods: laboratory: solid state - ISM: molecules -
techniques: spectroscopic - infrared: ISM
Abstract:
The molecular composition of interstellar ice mantles is defined by
gas-grain processes in molecular clouds, with the main components
being H2O, CO, and CO2. Methanol (CH3OH) ice is detected towards
the denser pre-stellar cores and star-forming regions, where large
amounts of CO molecules freeze out and get hydrogenated on top of the
icy grains. The thermal heating from nearby protostars can further
change the ice structure and composition. Despite the several
observations of icy features carried out towards molecular clouds and
along the line of site of protostars, it is not yet clear if
interstellar ices are mixed or if they have a layered structure.
We aim to examine the effect of mixed and layered ice growth in dust
grain mantle analogues, with specific focus on the position and shape
of methanol infrared bands, so dedicated future observations could
shed light on the structure of interstellar ices in different
environments.
Mixed and layered ice samples were deposited on a cold substrate kept
at a temperature of 10K using a closed-cycle cryostat placed in a
vacuum chamber. The spectroscopic features were analysed by Fourier
transform infrared spectroscopy. Different proportions of the most
abundant four molecular species in ice mantles, namely H2O, CO,
CO2, and CH3OH, were investigated, with a special attention placed
on the analysis of the CH3OH bands.
We measure changes in the position and shape of the CH and CO
stretching bands of CH3OH depending on the mixed or layered nature
of the ice sample. Spectroscopic features of methanol are also found
to change due to heating.
A layered ice structure best reproduces the CH3OH band position
recently observed towards a pre-stellar core and in star-forming
regions. Based on our experimental results, we conclude that
observations of CH3OH ice features in space can provide information
about the structure of interstellar ices, and we expect the James Webb
Space Telescope to put stringent constraints on the layered or mixed
nature of ices in different interstellar environments, from molecular
clouds to pre-stellar cores to protostars and protoplanetary discs.
Description:
We present the results of experiments with mixed and layered ices
containing H2O, CH3OH, CO and CO2 with an increasing number of
species in the ices. The absorption spectra were recorded for a KBr
substrate temperature of 10K and subsequent heating to a maximum
temperature of 100K. The spectral range lies between 4800-500cm-1.
All spectra were recorded with a resolution of 2cm-1.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 96 25 List of spectra of layered and mixed ice
sp/* . 25 Individual spectra of layered and mixed ice
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 26 A26 --- FileName Name of the spectrum file in subdirectory sp
28- 96 A69 --- Title Title of the file
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Byte-by-byte Description of file: sp/*
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Bytes Format Units Label Explanations
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1- 10 F10.5 cm-1 Wavenumber Wavenumber
12- 20 F9.6 --- Absorbance Absorbance
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Acknowledgements:
Birgitta Mueller, bmueller(at)mpe.mpg.de
(End) Birgitta Mueller [MPE], Patricia Vannier [CDS] 23-Jun-2021