J/A+A/653/A116 Methylamine mid-IR spectra in ice mixtures (Rachid+, 2021)
Infrared spectra of complex organic molecules in astronomically relevant ice
mixtures. IV. Methylamine.
Rachid M.G., Brunken N., de Boe D., Fedoseev G., Boogert A.C.A., Linnartz H.
<Astron. Astrophys. 653, A116 (2021)>
=2021A&A...653A.116R 2021A&A...653A.116R (SIMBAD/NED BibCode)
ADC_Keywords: Atomic physics
Keywords: astrochemistry - molecular data - methods: laboratory: molecular -
methods: laboratory: solid state - ISM: molecules -
techniques: spectroscopic
Abstract:
In the near future, high spatial and spectral infrared (IR) data of
star-forming regions obtained by the James Webb Space Telescope (JWST)
may reveal new solid-state features of various species, including more
intriguing classes of chemical compounds. The identification of
Complex organic molecules (COMs) in the upcoming data will only be
possible when laboratory IR ice spectra of these species under
astronomically relevant conditions are available for comparison. For
this purpose, systematic series of laboratory measurements are
performed, providing high-resolution IR spectra of COMs. Here, spectra
of pure methylamine (CH3NH2) and methylamine-containing ices are
discussed. The work is aimed at characterizing the mid-IR
(500-4000cm-1, 20-2.5 microns) spectra of methylamine in pure and
mixed ices to provide accurate spectroscopic data of vibrational bands
that are most suited to trace this species in interstellar ices.
Fourier transform infrared (FTIR) spectroscopy is used to record
spectra of CH3NH2 in the pure form and mixed with H2O, CH4,
and NH3, for temperatures ranging from 15 to 160K. The IR spectra in
combination with HeNe laser (632.8nm) interference data of pure
CH3NH2 ice was used to derive the IR band strengths of methylamine
in pure and mixed ices. The refractive index of amorphous methylamine
ice at 15K was determined as being 1.30±0.01. Accurate spectroscopic
information and band strength values are systematically presented for
a large set of methylamine-containing ices and different temperatures.
Selected bands are characterized and their use as methylamine tracers
is discussed. The selected bands include the following: the CH3
antisymmetric stretch band at 2881.3cm-1 (3.471 microns), the CH3
symmetric stretch band at 2791.9cm-1 (3.582 microns), the CH3
antisymmetric deformation bands, at 1455.0 and 1478.6cm-1 (6.873
microns and 6.761 microns), the CH_3 symmetric deformation band at
1420.3cm-1 (7.042 microns), and the CH3 rock at 1159.2cm-1
(8.621 microns). Using the laboratory data recorded in this work and
ground-based spectra of ices toward YSOs (Young Stellar Objects),
upper-limits for the methylamine ice abundances are derived. In some
of these YSOs, the methylamine abundance is less than 4 percent
relative to H2O.
Description:
Tables B1 to B15 list the peak position and FWHM of selected
methylamine features in pure and mixed ices at different temperatures.
Each table presents the data for a specific methylamine vibrational
mode in mixtures containing methylamine at the same dilution (1:5,
1:10, or 1:20). Tables B7, B8, and B9 present the data for two bands
(around 1455cm-1 and 1478cm-1) that are assigned to the CH3
antisym deformation mode of methylamine. In the cases in which these
modes overlap, the band profile is decomposed into two component
features and the FWHM and peak position are calculated for each of the
individual components. The absorption profile between 2800-2900cm-1
was decomposed into Gaussian features for the calculation of peak
position and FWHM for the CH3 antisymmetric stretch feature
(2881.3cm-1). In cases where the bands are weak or blended with
matrix bands, the FWHM is not determined, and a rough peak position is
given and marked with an asterisk (*). The resulting uncertainty is
much larger than the peak positions that are derived for features that
do not overlap.
Tables C1 to C15 present the integrated absorbance of the methylamine
bands (i.e., the band areas) in different ice mixtures and at selected
temperatures. Each table displays the data for one specific mixture.
The band's integrated absorption is normalized in relation to the
CH3 antisymmetric deformation mode, around 1478.6cm-1, from the
given mixture at 15K. The CH3 antisymmetric deformation mode was
chosen for normalization because this feature is distinguishable in
all the mixtures and does not overlap with any of the matrix
components.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tableb1.dat 68 28 CH3 rock(1159cm-1)-1:5 mixtures
tableb2.dat 68 56 CH3 rock(1159cm-1)-1:10 mixtures
tableb3.dat 68 49 CH3 rock(1159cm-1)-1:20 mixtures
tableb4.dat 68 30 CH3 sym def.(1420cm-1)-1:5 mixtures
tableb5.dat 68 58 CH3 sym def.(1420cm-1)-1:10 mixtures
tableb6.dat 68 44 CH3 sym def.(1420cm-1)-1:20 mixtures
tableb7.dat 68 51 CH3 antisym def.(1455 and 1478cm-1)-1:5 mixtures
tableb8.dat 68 103 CH3 antisym def.(1455 and 1478cm-1)-1:10 mixtures
tableb9.dat 68 95 CH3 antisym def.(1455 and 1478cm-1)-1:20 mixtures
tableb10.dat 68 21 CH3 sym stretch.(2791cm-1)-1:5 mixtures
tableb11.dat 68 37 CH3 sym stretch.(2791cm-1)-1:10 mixtures
tableb12.dat 68 33 CH3 sym stretch.(2791cm-1)-1:20 mixtures
tableb13.dat 69 28 CH3 antisym stretch.(2881cm-1)-1:5 mixtures
tableb14.dat 68 43 CH3 antisym stretch.(2881cm-1)-1:10 mixtures
tableb15.dat 68 33 CH3 antisym stretch.(2881cm-1)-1:20 mixtures
tablec.dat 57 98 Integrated absorbance for 15 different ice mixtures
(tables C1-C15)
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Byte-by-byte Description of file: tableb*.dat
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Bytes Format Units Label Explanations
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1- 36 A36 --- Ice Ice sample composition
38- 40 I3 K T Ice temperature
42- 48 F7.1 cm-1 Peak ? Peak position in cm-1
50- 55 F6.3 um Peakum ? Peak position in um
57- 61 F5.1 cm-1 FWHM ? FWHM in cm-1
63- 69 F7.4 um FWHMum ? FWHM in um
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Byte-by-byte Description of file: tablec.dat
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Bytes Format Units Label Explanations
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1- 24 A24 --- Ice Ice mixture
25- 27 I3 K T Ice temperature
29- 32 F4.2 --- R1 ? Ratio between the area of the 1159cm-1 feature
in ice mixture at temperature T and the
area of the 1478cm-1 feature in the ice at 15K
34- 37 F4.2 --- R2 ? Ratio between the area of the 1420cm-1 feature
in ice mixture at temperature T and the
area of the 1478cm-1 feature in the ice at 15K
39- 42 F4.2 --- R3 Ratio between the area of the 1455cm-1 feature
in ice mixture at temperature T and the
area of the 1478cm-1 feature in the ice at 15K
44- 47 F4.2 --- R4 Ratio between the area of the 1478cm-1 feature
in ice mixture at temperature T and the
area of the 1478cm-1 feature in the ice at 15K
49- 52 F4.2 --- R5 ? Ratio between the area of the 2792cm-1 feature
in ice mixture at temperature T and the
area of the 1478cm-1 feature in the ice at 15K
54- 57 F4.2 --- R6 ? Ratio between the area of the 2881cm-1 feature
in ice mixture at temperature T and the
area of the 1478cm-1 feature in the ice at 15K
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Acknowledgements:
Marina Gomes Rachid, rachid(at)strw.leidenuniv.nl,
marina.g.rachid(at)gmail.com
References:
Terwisscha van Scheltinga et al., Paper I 2018A&A...611A..35T 2018A&A...611A..35T
Rachid et al., Paper II 2020A&A...639A...4R 2020A&A...639A...4R
Terwisscha van Scheltinga et al., Paper III A&A, in prep.
(End) Marina G. Rachid [Leiden Obs.], Patricia Vannier [CDS] 01-Jul-2021