J/A+A/677/A65 Methylamine vt=1 (Gyawali+, 2023)
Rotational spectrum and interstellar detection of the first torsionally excited
state of methylamine.
Gyawali P., Motiyenko R.A., Belloche A., Kleiner I., Ilyushin V.V.,
Alekseev E.A., Gulaczyk I., Kreglewski M.
<Astron. Astrophys. 677, A65 (2023)>
=2023A&A...677A..65G 2023A&A...677A..65G (SIMBAD/NED BibCode)
ADC_Keywords: Spectra, millimetric/submm ; Spectroscopy ; Molecular clouds
Keywords: ISM: molecules - methods: laboratory: molecular - submillimeter: ISM -
molecular data - line: identification
Abstract:
Methylamine (CH3NH2) was first detected in the interstellar medium
(ISM) toward Sgr B2 almost 50 years ago by observation of rotational
transitions in its torsional ground state. Methylamine exhibits two
large-amplitude motions (LAMs), the methyl torsion and amine wagging,
which complicate the spectral analysis, especially in excited
vibration states. The lack of an accurate model of the two coupled
LAMs has also hampered the identification in the ISM of rotational
transitions in excited vibrational states.
The aim of this work is to study the terahertz and microwave
rotational spectra of methylamine experimentally and theoretically in
order to provide a reliable basis for the detection of its rotational
transitions in the first torsionally excited state, vt=1, in the
ISM.
The terahertz spectrum of methylamine was measured from 150 to 1520GHz
with the Lille fast scan spectrometer. Using a new "hybrid"
Hamiltonian model, we were able to analyze the nuclear quadrupole
hyperfine structure and to accurately fit the rotational spectrum of
the vt=1 state of methylamine. We used the imaging spectral line
survey ReMoCA performed with the Atacama Large
Millimeter/submillimeter Array (ALMA) to search for rotational
transitions of methylamine in its first torsionally excited state
toward the high-mass star forming region Sgr B2(N). The observed
spectra are modeled under the assumption of local thermodynamic
equilibrium (LTE).
Accurate spectral predictions were obtained for the ground and first
excited states of CH3NH2. We report the first interstellar
detection of methylamine in the vt=1 state toward the offset
position Sgr B2(N1S) in the hot molecular core Sgr B2(N1). The LTE
parameters derived previously from the rotational emission of
methylamine in its torsional ground state toward Sgr B2(N1S) yield
synthetic spectra of methylamine in the vt=1 state that are fully
consistent with the ALMA spectra and allow us to identify five
rotational lines of this state.
Description:
We provide the lists of rotational and rovibrational transitions of
methylamine used in the least-squares fitting.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tableb1.dat 66 6484 Measured pure rotational transitions
of methylamine
tableb2.dat 66 27736 Measured rovibrational transitions of methylamine
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See also:
J/A+A/563/A137 : THz spectrum of methylamine (Motiyenko+, 2014)
Byte-by-byte Description of file: tableb1.dat
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Bytes Format Units Label Explanations
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2 I1 --- v" Upper v quantum number
3- 6 I4 --- J" Upper J quantum number
7- 10 I4 --- Ka" Upper Ka quantum number
11- 14 I4 --- Kc" Upper Kc quantum number
15- 17 A3 --- S" Upper symmetry label
19 I1 --- v' Lower v quantum number
20- 23 I4 --- J' Lower J quantum number
24- 27 I4 --- Ka' Lower Ka quantum number
28- 31 I4 --- Kc' Lower Kc quantum number
32- 34 A3 --- S' Lower symmetry label
35- 48 F14.3 MHz Freq Observed transition frequency
49- 55 F7.3 MHz unc Mesaurement uncertainty
56- 62 F7.3 MHz O-C Individual residuals of the fit
63- 64 I2 --- Incl [0/1] Flag for included (1) or
excluded (0) transition in the fit
66 I1 --- Ref [1/5] Bibiliographic reference indicator (1)
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Note (1): References as follows:
1 = this study
2 = Motiyenko et al. (2014A&A...563A.137M 2014A&A...563A.137M, Cat. J/A+A/563/A137)
3 = Ohashi et al. (1989, J. Mol. Spectrosc., 137, 33)
4 = Kreglewski & Wlodarczak (1992, J. Mol. Spectrosc., 156, 393)
5 = Motiyenko (2007, private communication)
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Byte-by-byte Description of file: tableb2.dat
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Bytes Format Units Label Explanations
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2 I1 --- v" Upper v quantum number
4- 6 I3 --- J" Upper J quantum number
8- 10 I3 --- Ka" Upper Ka quantum number
12- 14 I3 --- Kc" Upper Kc quantum number
16- 17 A2 --- S" Upper symmetry label
19 I1 --- v' Lower v quantum number
21- 23 I3 --- J' Lower J quantum number
25- 27 I3 --- Ka' Lower Ka quantum number
29- 31 I3 --- Kc' Lower Kc quantum number
33- 34 A2 --- S' Lower symmetry label
37- 46 F10.4 cm-1 Freq Observed transition frequency
49- 54 F6.4 cm-1 unc Mesaurement uncertainty
55- 62 F8.4 cm-1 O-C Individual residuals of the fit
64 A1 --- K=2 [L] Optional flag for vt=2-1 and vt=1-0
transitions of A1,A2,B1 and B2 symmetries (1)
66 I1 --- Incl [0/1] Flag for included (1) or
excluded (0) transition
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Note (1): The flag indicates that the Ka=2 and Ka=4 labels are reversed
compared to the labels from Gulaczyk & Kreglewski (2020,
J. Quant. Spectr. Rad. Transf., 217, 321).
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Acknowledgements:
Roman Motiyenko, roman.motiyenko(at)univ-lille.fr
(End) Roman Motiyenko [PhLAM, Univ. Lille], Patricia Vannier [CDS] 18-Jul-2023