J/A+A/641/A160 Hot aminoacetonitrile in Sgr B2 (Melosso+, 2020)
Far-infrared laboratory spectroscopy of aminoacetonitrile and first interstellar
detection of its vibrationally excited transitions.
Melosso M., Belloche A., Martin-Drumel M.A., Pirali O., Tamassia F.,
Bizzocchi L., Garrod R.T., Muller H.S.P., Menten K.M., Dore L., Puzzarini C.
<Astron. Astrophys. 641, A160 (2020)>
=2020A&A...641A.160M 2020A&A...641A.160M (SIMBAD/NED BibCode)
ADC_Keywords: Atomic physics ; Spectroscopy
Keywords: methods: laboratory: molecular - techniques: spectroscopic -
astrochemistry - ISM: molecules - line: identification -
ISM: abundances
Abstract:
Aminoacetonitrile, a molecule detected in the interstellar medium only
towards the star-forming region Sagittarius B2 (Sgr B2) thus far, is
considered an important prebiotic species; in particular it is a
possible precursor of the simplest amino acid glycine. To date,
observations were limited to ground state emission lines, whereas
transitions from within vibrationally excited states remained
undetected.
We wanted to accurately determine the energies of the low-lying
vibrational states of aminoacetonitrile, which are expected to be
populated in Sgr B2(N1), the main hot core of Sgr B2(N). This step is
fundamental in order to properly evaluate the vibration-rotation
partition function of aminoacetonitrile as well as the line strengths
of the rotational transitions of its vibrationally excited states.
This is necessary to derive accurate column densities and secure the
identification of these transitions in astronomical spectra.
The far-infrared ro-vibrational spectrum of aminoacetonitrile has been
recorded in absorption against a synchrotron source of continuum
emission. Three bands, corresponding to the lowest vibrational modes
of aminoacetonitrile, were observed in the frequency region below
500cm-1. The combined analysis of ro-vibrational and pure rotational
data allowed us to prepare new spectral line catalogs for all the
states under investigation. We used the imaging spectral line survey
ReMoCA performed with ALMA to search for vibrationally excited
aminoacetonitrile toward Sgr B2(N1). The astronomical spectra were
analyzed under the local thermodynamic equilibrium (LTE)
approximation.
Almost 11000 lines have been assigned during the analysis of the
laboratory spectrum of aminoacetonitrile, thanks to which the
vibrational energies of the v11=1, v18=1, and v17=1 states have
been determined. The whole dataset, which includes high J and Ka
transitions, is well reproduced within the experimental accuracy.
Reliable spectral predictions of pure rotational lines can now be
produced up to the THz region. On the basis of these spectroscopic
predictions, we report the interstellar detection of aminoacetonitrile
in its v11=1 and v18=1 vibrational states toward Sgr B2(N1)
in addition to emission in its vibrational ground state. The
intensities of the identified v11=1 and v18=1 lines are
consistent with the detected v=0 lines under LTE at a temperature
of 200K for an aminoacetonitrile column density of 1.1x1017/cm2.
This work shows the strong interplay between laboratory spectroscopy
exploiting (sub)millimeter and synchrotron far-infrared techniques,
and observational spectral surveys to detect complex organic molecules
in space and quantify their abundances.
Description:
This work presents (i) the first analysis of the high-resolution
ro-vibrational spectrum of aminoacetonitrile, where the three lowest
excited states are observed and (ii) the search for vibrationally
excited aminoacetonitrile with ALMA using the ReMoCA survey. The list
of observed ro-vibrational transition frequencies is provided as
article data in the electronic table s1.dat, which resembles the .lin
input file of SPFIT. More details about SPFIT can be found at
https://cdms.astro.uni-koeln.de/classic/general or at
http://www.ifpan.edu.pl/~kisiel/asym/pickett/crib.htm
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tables1.dat 61 13261 Measured ro-vibrational transitions for
aminoacetonitrile with FT-IR spectroscopy
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See also:
J/ApJS/209/23 : Aminoacetonitrile transition frequencies (Motoki+, 2013)
J/ApJS/229/26 : Rotational spectra of aminoacetonitrile (Kolesnikova+, 2017)
J/ApJS/230/26 : NH2CH2CN transition frequencies (Degli Esposti+, 2017)
Byte-by-byte Description of file: tables1.dat
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Bytes Format Units Label Explanations
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2- 3 I2 --- J' Quantum number J for upper level
5- 6 I2 --- Ka' Quantum number Ka for upper level
8- 9 I2 --- Kc' Quantum number Kc for upper level
12 I1 --- v' [0/3] Quantum number v for upper level (1)
14- 15 I2 --- J" Quantum number J for lower level
17- 18 I2 --- Ka" Quantum number Ka for lower level
20- 21 I2 --- Kc" Quantum number Kc for lower level
24 I1 --- v" [0/3] Quantum number v for lower level (1)
41- 50 F10.6 cm-1 Freq Measured frequency
54- 61 F8.5 cm-1 Uncert Uncertainty associated to frequency (2)
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Note (1): 0 is ground state, 1 is v11=1, 2 is v18=1, and 3 is v17=1;
Note (2): The minus sign follows the SPFIT format for the use of wavenumber
units.
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Acknowledgements:
Mattia Melosso, mattia.melosso2(at)unibo.it
(End) Patricia Vannier [CDS] 23-Jun-2020