J/A+A/666/A50 Rotational spectrum of vinylisocyanate (Vavra+, 2022)
Millimeter wave spectrum and search for vinyl isocyanate toward Sgr B2(N)
with ALMA.
Vavra K., Kolesnikova L., Belloche A., Garrod R.T., Koucky J., Uhlikova T.,
Lukova K., Guillemin J.-C., Kania P., Muller H.S.P., Menten K.M., Urban S.
<Astron. Astrophys. 666, A50 (2022)>
=2022A&A...666A..50V 2022A&A...666A..50V (SIMBAD/NED BibCode)
ADC_Keywords: Atomic physics ; Interstellar medium ; Spectroscopy
Keywords: astrochemistry - ISM: molecules - line: identification -
ISM: individual objects: Sagittarius B2 -
methods: laboratory: molecular
Abstract:
The interstellar detections of isocyanic acid (HNCO), methyl
isocyanate (CH3NCO), and very recently also ethyl isocyanate
(C2H5NCO) invite the question of whether or not vinyl isocyanate
(C2H3NCO) can be detected in the interstellar medium. There are
only low-frequency spectroscopic data (<40GHz) available for this
species in the literature, which makes predictions at higher
frequencies rather uncertain, which in turn hampers searches for this
molecule in space using millimeter (mm) wave astronomy.
The aim of the present study is on one hand to extend the laboratory
rotational spectrum of vinyl isocyanate to the mm wave region and on
the other to search, for the first time, for its presence in the
high-mass star-forming region Sgr B2, where other isocyanates and a
plethora of complex organic molecules are observed.
We recorded the pure rotational spectrum of vinyl isocyanate in the
frequency regions 127.5-218 and 285-330GHz using the Prague mm wave
spectrometer. The spectral analysis was supported by high-level
quantum-chemical calculations. On the astronomy side, we assumed local
thermodynamic equilibrium to compute synthetic spectra of vinyl
isocyanate and to search for it in the ReMoCA survey performed with
the Atacama Large Millimeter/submillimeter Array (ALMA) toward the
high-mass star-forming protocluster Sgr B2(N). Additionally, we
searched for the related molecule ethyl isocyanate in the same source.
Accurate values for the rotational and centrifugal distortion
constants are reported for the ground vibrational states of trans and
cis vinyl isocyanate from the analysis of more than 1000 transitions.
We report nondetections of vinyl and ethyl isocyanate toward the main
hot core of Sgr B2(N). We find that vinyl and ethyl isocyanate are at
least 11 and 3 times less abundant than methyl isocyanate in this
source, respectively.
Although the precise formation mechanism of interstellar methyl
isocyanate itself remains uncertain, we infer from existing
astrochemical models that our observational upper limit for the
CH3NCO:C2H5NCO ratio in Sgr B2(N) is consistent with ethyl
isocyanate being formed on dust grains via the abstraction or
photodissociation of an H atom from methyl isocyanate, followed by the
addition of a methyl radical. The dominance of such a process for
ethyl isocyanate production, combined with the absence of an analogous
mechanism for vinyl isocyanate, would indicate that the ratio
C2H3NCO:C2H5NCO should be less than unity. Even though vinyl
isocyanate was not detected toward Sgr B2(N), the results of this work
represent a significant improvement on previous low-frequency studies
and will help the astronomical community to continue searching for
this species in the Universe.
Description:
List of measured transitions of trans and cis vinyl isocyanate.
JPL/CDMS catalog line list for trans and cis vinyl isocyanate.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea2.dat 100 520 List of the measured transitions of
trans vinyl isocyanate
tablea3.dat 102 892 List of the measured transitions of
cis vinyl isocyanate
tablea5.dat 73 6876 JPL/CDMS catalog line list for
trans vinyl isocyanate
tablea6.dat 73 5279 JPL/CDMS catalog line list for
cis vinyl isocyanate
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Byte-by-byte Description of file:tablea2.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- J' Upper state J quantum number
4- 6 I3 --- Ka' Upper state Ka quantum number
7- 9 I3 --- Kc' Upper state Kc quantum number
12- 14 I3 --- J" Lower state J quantum number
15- 17 I3 --- Ka" Lower state Ka quantum number
18- 20 I3 --- Kc" Lower state Kc quantum number
33- 43 F11.4 MHz FreqObs Observed transition frequency
46- 52 F7.4 MHz O-C Observed minus calculated frequency
55- 59 F5.3 MHz e_Freq Experimental uncertainty
62- 68 F7.4 MHz (O-C)b ? Observed minus calculated frequency
for blends
70- 73 F4.2 --- wb ? Weight of the components of the blends
81-100 A20 --- Notes Source of the data (G1)
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Byte-by-byte Description of file: tablea3.dat
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Bytes Format Units Label Explanations
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2- 3 I2 --- J' Upper state J quantum number
5- 6 I2 --- Ka' Upper state Ka quantum number
8- 9 I2 --- Kc' Upper state Kc quantum number
13- 14 I2 --- J" Lower state J quantum number
16- 17 I2 --- Ka" Lower state Ka quantum number
19- 20 I2 --- Kc" Lower state Kc quantum number
33- 43 F11.4 MHz FreqObs Observed transition frequency
46- 52 F7.4 MHz O-C Observed minus calculated frequency
55- 59 F5.3 MHz e_Freq Experimental uncertainty
62- 68 F7.4 MHz (O-C)b ? Observed minus calculated frequency
for blends
70- 73 F4.2 --- wb ? Weight of the components of the blends
81-102 A22 --- Notes Source of the data (G1)
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Byte-by-byte Description of file: tablea5.dat
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Bytes Format Units Label Explanations
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3- 13 F11.4 MHz Freq Frequency (1)
16- 21 F6.4 MHz e_Freq Uncertainty of the frequency
23- 29 F7.4 [nm2.MHz] log(Int) Base 10 logarithm of the integrated
intensity in units of nm2 MHz at 300K
31 I1 --- DR Degrees of freedom in the rotational
partition function
33- 41 F9.4 cm-1 Elow Energy of the lower level
42- 44 I3 --- gupp Upper state degeneracy
47- 51 I5 --- TAG Species tag or molecular identifier
53- 55 I3 --- QNFMT Format of the quantum numbers
56- 57 A2 --- J' Upper state J quantum number
58- 59 I2 --- Ka' Upper state Ka quantum number
60- 61 A2 --- Kc' Upper state Kc quantum number
68- 69 A2 --- J" Lower state J quantum number
70- 71 I2 --- Ka" Lower state Ka quantum number
72- 73 A2 --- Kc" Lower state Kc quantum number
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Note (1): The key parameters used in the generation of this table:
mu_a = 2.047 D, mu_b = 0.824 D, T = 300 K, and Qrot = 62500.3370 which
takes into account the ground vibrational states of both isomers.
Predictions of a-type transitions should be reliable up to
J = 68 for Ka = 0 - 5 and J = 44 for Ka = 6, which correspond to the data
sets encompassed in this work and interpolations between them.
Predictions with Ka > 6 are not recommended for use and Ka < 6 beyond 330 GHz
should be viewed with caution due to possible perturbations.
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Byte-by-byte Description of file: tablea6.dat
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Bytes Format Units Label Explanations
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3- 13 F11.4 MHz Freq Frequency (2)
15- 21 F7.4 MHz e_Freq Uncertainty of the frequency
23- 29 F7.4 [nm2.MHz] log(Int) Base 10 logarithm of the integrated
intensity in units of nm2 MHz at 300K
31 I1 --- DR Degrees of freedom in the rotational
partition function
33- 41 F9.4 cm-1 Elow Energy of the lower level
42- 44 I3 --- gupp Upper state degeneracy
47- 51 I5 --- TAG Species tag or molecular identifier
53- 55 I3 --- QNFMT Format of the quantum numbers
56- 57 I2 --- J' Upper state J quantum number
58- 59 I2 --- Ka' Upper state Ka quantum number
60- 61 I2 --- Kc' Upper state Kc quantum number
68- 69 I2 --- J" Lower state J quantum number
70- 71 I2 --- Ka" Lower state Ka quantum number
72- 73 I2 --- Kc" Lower state Kc quantum number
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Note (2): The key parameters used in the generation of this table:
mu_a = 2.14 D, mu_b = 0.09 D, T = 300 K, Qrot = 62500.3370 which takes into
account the ground vibrational states of both isomers, and E = 301 cm-1.
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Global notes:
Note (G1): References as follows:
Kirby & Kroto (1978): 1978, J. Mol. Spectrosc., 70, 216.
Bouchy & Roussy (1977): 1977, J. Mol. Spectrosc., 68, 156.
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Acknowledgements:
Lucie Kolesnikova, lucie.kolesnikova(at)vscht.cz
(End) L. Kolesnikova [UCT Prague, Czech Republic], P. Vannier [CDS] 26-Sep-2022