J/A+A/601/A49 CH3NHCHO rotational spectroscopy (Belloche+, 2017)
Rotational spectroscopy, tentative interstellar detection, and chemical
modelling of N-methylformamide.
Belloche A., Meshcheryakov A.A., Garrod R.T., Ilyushin V.V., Alekseev E.A.,
Motiyenko R.A., Margules L., Mueller H.S.P., Menten K.M.
<Astron. Astrophys. 601, A49 (2017)>
=2017A&A...601A..49B 2017A&A...601A..49B (SIMBAD/NED BibCode)
ADC_Keywords: Atomic physics ; Interstellar medium
Keywords: line: identification - molecular data - radio lines: ISM -
ISM: molecules - ISM: individual objects: Sagittarius B2(N) -
astrochemistry -
Abstract:
N-methylformamide, CH3NHCHO, may be an important molecule for
interstellar pre-biotic chemistry because it contains a peptide bond,
which in terrestrial chemistry is responsible for linking amino acids
in proteins. The rotational spectrum of the most stable trans
conformer of N-methylformamide is complicated by strong
torsion-rotation interaction due to the low barrier of the methyl
torsion. For this reason, the theoretical description of the
rotational spectrum of the trans conformer has up to now not been
accurate enough to provide a firm basis for its interstellar
detection.
In this context, as a prerequisite for a successful interstellar
detection, our goal is to improve the characterization of the
rotational spectrum of N-methylformamide.
We use two absorption spectrometers in Kharkiv and Lille to measure
the rotational spectra over the frequency range 45-630 GHz. The
analysis is carried out using the Rho-axis method and the RAM36 code.
We search for N-methylformamide toward the hot molecular core
Sagittarius (Sgr) B2(N2) using a spectral line survey carried out with
the Atacama Large Millimeter/submillimeter Array (ALMA). The
astronomical spectra are analyzed under the assumption of local
thermodynamic equilibrium. The astronomical results are put into a
broader astrochemical context with the help of a gas-grain chemical
kinetics model.
The new laboratory data set for the trans conformer of
N-methylformamide consists of 9469 distinct line frequencies with
J≤62, including the first assignment of the rotational spectra of the
first and second excited torsional states. All these lines are fitted
within experimental accuracy for the first time. Based on the reliable
frequency predictions obtained in this study, we report the tentative
detection of N-methylformamide towards Sgr B2(N2). We find
N-methylformamide to be more than one order of magnitude less abundant
than formamide (NH2CHO), a factor of two less abundant than the
unsaturated molecule methyl isocyanate (CH3NCO), but only slightly
less abundant than acetamide (CH3CONH2). We also report the
tentative detection of the 15N isotopologue of formamide
(15NH2CHO) toward Sgr B2(N2). The chemical models indicate that
the efficient formation of HNCO via NH + CO on grains is a necessary
step in the achievement of the observed gas-phase abundance of
CH3NCO. Production of CH3NHCHO may plausibly occur on grains
either through the direct addition of functional-group radicals or
through the hydrogenation of CH3NCO. Conclusions. Provided the
detection of N-methylformamide is confirmed, the only slight
underabundance of this molecule compared to its more stable structural
isomer acetamide and the sensitivity of the model abundances to the
chemical kinetics parameters suggest that the formation of these two
molecules is controlled by kinetics rather than thermal equilibrium.
Description:
Table 2 contains the final data set of fitted transitions of the
N-methylformamide trans conformer. Table 3 predictions of rotational
transitions of trans N-methylformamide in the vt = 0, 1, and 2
torsionally excited states resulting from the fit. The predictions are
calculated for the frequency range up to 650GHz and for the
transitions with J≤65.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 76 12456 Assigned rotational transitions of the ground and
v5=1 excited vibrational states of carbonyl cyanide
table3.dat 91 182933 Predicted rotational transitions of the ground
vibrational state of carbonyl cyanide up to 1THz
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See also:
J/A+A/493/565 : Deuterated and 15N ethyl cyanides (Margules+, 2009)
J/A+A/538/A51 : Rotational spectrum of CH3CH(NH2)CN (Mollendal+, 2012)
J/A+A/538/A119 : Spectrum of 18O-methyl formate (HCO18OCH3) (Tercero+ 20
J/A+A/540/A51 : Submm spectrum of deuterated glycolaldehydes (Bouchez+, 2012)
J/A+A/543/A46 : Submillimeter spectrum of HCOOCD2H (Coudert+, 2012)
J/A+A/543/A135 : New analysis of 13C-CH3CH2CN up to 1THz (Richard+, 2012)
J/A+A/544/A82 : Rotational spectroscopy of diisocyanomethane (Motiyenko+ 2012)
J/A+A/548/A71 : Spectroscopy and ISM detection of formamide (Motiyenko+, 2012)
J/A+A/549/A96 : mm and sub-mm spectra of 13C-glycolaldehydes (Haykal+ 2013)
J/A+A/549/A128 : Singly deuterated isotopologues of formamide (Kutsenko+, 2013)
J/A+A/552/A117 : Mono-deuterated dimethyl ether (Richard+, 2013)
J/A+A/553/A84 : (Sub)mm spectrum of deuterated methyl cyanides (Nguyen+, 2013)
J/A+A/559/A44 : Rotational spectrum of MAAN (CH2NCH2CN) (Motiyenko+, 2013)
J/ApJ/779/119 : HCOOCH2D detection in Orion KL (Coudert+, 2013)
J/A+A/563/A137 : THz spectrum of methylamine (Motiyenko+, 2014)
J/A+A/568/A58 : HCOO13CH3 rotational spectrum (Haykal+, 2014)
J/A+A/579/A46 : Mono-13C acetaldehydes mm/submm spectra (Margules+ 2015)
J/A+A/587/A152 : Rotational spectrum of 13C methylamine (Motiyenko+, 2016)
J/A+A/590/A93 : Doubly 13C-substituted ethyl cyanide (Margules+, 2016)
J/A+A/592/A43 : Millimeter wave spectra of carbonyl cyanide (Bteich+, 2016)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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3- 4 I2 --- m0 Upper m quantum number
7- 10 F4.1 --- F0 ? Upper F quantum number
13- 14 I2 --- J0 Upper J quantum number
17- 18 I2 --- Ka0 Upper Ka quantum number
21- 22 I2 --- Kc0 Upper Kc quantum number
25- 26 I2 --- m1 Lower m quantum number
29- 32 F4.1 --- F1 ? Lower F quantum number
35- 36 I2 --- J1 Lower J quantum number
39- 40 I2 --- Ka1 Lower Ka quantum number
43- 44 I2 --- Kc1 Lower Kc quantum number
46- 58 F13.4 MHz Freq Observed transition frequency
61- 67 F7.4 MHz unc Uncertainty of measurements
69- 76 F8.4 MHz O-C Residuals of the fit
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
3- 4 I2 --- m0 Upper m quantum number
7- 10 F4.1 --- F0 Upper F quantum number
13- 14 I2 --- J0 Upper J quantum number
17- 18 I2 --- Ka0 Upper Ka quantum number
21- 22 I2 --- Kc0 Upper Kc quantum number
25- 26 I2 --- m1 Lower m quantum number
29- 32 F4.1 --- F1 Lower F quantum number
35- 36 I2 --- J1 Lower J quantum number
39- 40 I2 --- Ka1 Lower Ka quantum number
43- 44 I2 --- Kc1 Lower Kc quantum number
48- 58 F11.4 MHz Freq Predicted transition frequency
61- 66 F6.4 MHz Unc Uncertainty of predicted transition frequency
69- 78 F10.4 cm-1 Elo The energy of the lower state
82- 91 E10.4 D+2 Smu2 Product mu^2*S
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Acknowledgements:
Roman Motiyenko, roman.motienko(at)univ-lille1.fr
(End) Roman Motiyenko [PhLAM, Lille 1], Patricia Vannier [CDS] 19-Jan-2017