J/A+A/668/A46 Laboratory spectroscopy of theoretical ices (Mueller+ 2022)
Laboratory spectroscopy of theoretical ices:
Predictions for JWST and test for astrochemical models.
Mueller B., Giuliano B.M., Vasyunin A., Fedoseev G., Caselli P.
<Astron. Astrophys. 668, A46 (2022)>
=2022A&A...668A..46M 2022A&A...668A..46M (SIMBAD/NED BibCode)
ADC_Keywords: Spectra, infrared ; Spectroscopy
Keywords: astrochemistry - methods: laboratory: solid state -
ISM: molecules - techniques: spectroscopic - infrared: ISM
Abstract:
The pre-stellar core L1544 has been the subject of several
observations conducted in the past years, complemented by modelling
studies focused on its gas and ice-grain chemistry. The chemical
composition of the ice mantles reflects the environmental physical
changes along the temporal evolution, such as density and temperature.
The investigation outcome hints at a layered structure of interstellar
ices with abundance of H2O in the inner layers and an increasing
concentration of CO near the surface. The morphology of interstellar
ice analogues can be investigated experimentally assuming a
composition derived from chemical models.
This research presents a new approach of a three-dimensional fit where
observational results are first fitted with a gas-grain chemical model
predicting the exact ice composition including infrared (IR) inactive
species. Then the laboratory IR spectra are recorded for interstellar
ice analogues whose compositions reflect the obtained numerical
results, in a layered and in a mixed morphology. These results could
then be compared with the results of James Webb Space Telescope (JWST)
observations. Special attention is paid to the inclusion of IR
inactive species whose presence is predicted in the ice, but is
typically omitted in the laboratory obtained data. This stands for N2,
one of the main possible constituents of interstellar ice mantles, and
O2.
Ice analogue spectra were recorded at a temperature of 10K using a
Fourier transform infrared spectrometer. In the case of layered ice we
deposited a H2O-CO-N2-O2 mixture on top of a H2O-CH3OH-N2
ice, while in the case of mixed ice we examined a
H2O-CH3OH-N2-CO composition. The selected species are the four
most abundant ice components predicted by the chemical model. Results.
Following the changing composition and structure of the ice, we find
differences in the absorption bands for most of the examined
vibrational modes. The extent of observed changes in the IR band
profiles will allow us to analyse the structure of ice mantles in
L1544 from future observations by the JWST.
Our spectroscopic measurements of interstellar ice analogues predicted
by our well-received gas-grain chemical codes of pre-stellar cores
will allow detailed comparison with upcoming JWST observations. This
is crucial in order to put stringent constraints on the chemical and
physical structure of dust icy mantles just before the formation of
stars and protoplanetary disks, and to explain surface chemistry.
Description:
We present the results of experiments with mixed and layered ices
containing H2O, CH3OH, CO, N2 and O2 whose compositions
reflect the obtained numerical results of a gas-grain chemical mode.
The absorption spectra were recorded for a KBr substrate temperature
of 10K. The spectral range lies between 4800-500cm-1. All spectra
were recorded with a resolution of 1cm-1.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
elayer1.dat 20 8919 Layer 1, H2O:CH3OH:N2 = 100%:67.5%:27.5%
elayer2.dat 20 8919 Layer 2, H2O:N2:CO:O2 = 100%:46%:146%:38%
elayer21.dat 20 8919 Layer 2 on top of Layer 1
emixed.dat 20 8919 Mixed, H2O:CH3OH:N2:CO = 100%:58%:29%:37
mlaymfr.dat 112 162 Predicted molecular fractional abundances for
each layer
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See also:
J/A+A/620/A46 : O2 signature in thin and thick O2-H2O ices (Mueller+, 2018)
J/A+A/629/A112 : Complex refractive index of CO ice (Giuliano+, 2019)
J/A+A/652/A126 : Spectroscopy of CH3OH in layered & mixed ices (Mueller+, 2021)
Byte-by-byte Description of file: elayer*.dat emixed.dat
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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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Byte-by-byte Description of file: mlaymfr.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- ML [0/161] Number of the monolayer
7- 16 E10.4 --- bH2O H2O fraction of a monolayer
19- 28 E10.4 --- bCH4O CH3OH fraction of a monolayer
31- 40 E10.4 --- bCO CO fraction of a monolayer
43- 52 E10.4 --- bN2 N2 fraction of a monolayer
55- 64 E10.4 --- bH2CO H2CO fraction of a monolayer
67- 76 E10.4 --- bNH3 NH3 fraction of a monolayer
79- 88 E10.4 --- bH2 H2 fraction of a monolayer
91-100 E10.4 --- bH2O2 H2O2 fraction of a monolayer
103-112 E10.4 --- bO2 O2 fraction of a monolayer
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Acknowledgements:
Birgitta Mueller, bmueller(at)mpe.mpg.de
(End) Birgitta Mueller [MPE], Patricia Vannier [CDS] 29-Jul-2022