J/A+A/666/A114 n- and i-butanal rotational spectroscopy (Sanz-Novo+, 2022)
Toward the limits of complexity of interstellar chemistry:
Rotational spectroscopy and astronomical search for n- and i-butanal.
Sanz-Novo M., Belloche A., Rivilla V.M., Garrod R.T., Alonso J.L.,
Redondo P., Barrientos C., Kolesnikova L., Valle J.C., Rodriguez-Almeida L.,
Jimenez-Serra I., Martin-Pintado J., Muller H.S.P., Menten K.
<Astron. Astrophys. 666, A114 (2022)>
=2022A&A...666A.114S 2022A&A...666A.114S (SIMBAD/NED BibCode)
ADC_Keywords: Interstellar medium ; Spectroscopy ; Atomic physics
Keywords: ISM: molecules - molecular data - astrochemistry -
line: identification - ISM: individual objects: Sagittarius B2 -
ISM: individual objects: G+0.693-0.027
Abstract:
In recent times, large organic molecules of exceptional complexity
have been found in diverse regions of the interstellar medium.
In this context, we aim to provide accurate frequencies of the ground
vibrational state of two key aliphatic aldehydes, n-butanal and its
branched- chain isomer, i-butanal, to enable their eventual detection
in the interstellar medium. We also want to test the level of
complexity that interstellar chemistry can reach in regions of star
formation.
We employ a frequency modulation millimeter- and submillimeter-wave
absorption spectrometer to measure the rotational features of n- and
i-butanal. We analyze the assigned rotational transitions of each
rotamer separately using the A-reduced semirigid-rotor Hamiltonian. We
use the spectral line survey REMoCA performed with the Atacama Large
Millimeter/submillimeter Array to search for n- and i-butanal toward
the star forming region Sgr B2(N). We also search for both aldehydes
toward the molecular cloud G+0.693-0.027 with IRAM 30m and Yebes 40 m
observations. The observational results are compared with
computational results from a recent gas-grain astrochemical model.
Several thousands of rotational transitions belonging to the
lowest-energy conformers of two distinct linear and branched isomers
have been assigned in the laboratory spectra up to 325 GHz. A precise
set of the relevant rotational spectroscopic constants has been
determined for each structure as a first step to identifying both
molecules in the interstellar medium. We report nondetections of n-
and i-butanal toward both sources Sgr B2(N1S) and G+0.693-0.027. We
find that n- and i-butanal are at least 2-6 and 6-18 times less
abundant than acetaldehyde toward Sgr B2(N1S), respectively, and that
n-butanal is at least 63 times less abundant than acetaldehyde toward
G+0.693-0.027. While propanal is not detected toward Sgr B2(N1S)
either, with an abundance at least 5-11 lower than that of
acetaldehyde, propanal is found to be 7 times less abundant than
acetaldehyde in G+0.693-0.027. Comparison with astrochemical models
indicates good agreement between observed and simulated abundances
(where available). Grain-surface chemistry appears sufficient to
reproduce aldehyde ratios in G+0.693-0.027; gas-phase production may
play a more active role in Sgr B2(N1S). Model estimates for the larger
aldehydes indicate that the observed upper limits may be close to the
underlying values.
Our astronomical results indicate that the family of interstellar
aldehydes in the Galactic center region is characterized by a drop of
one order of magnitude in abundance at each incrementation in the
level of molecular complexity.
Description:
Complete list of transitions of cis-gauche n-butanal in the ground
state.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
cgprcho.dat 135 2839 Fitted rotational transitions of
cg-nPrCHO in the ground state
ctnprcho.dat 135 1375 Fitted rotational transitions of
ct-nPrCHO in the ground state
giprcho.dat 135 3411 Fitted rotational transitions of
g-iPrCHO in the ground state
tiprcho.dat 135 513 Fitted rotational transitions of
t-iPrCHO in the ground state
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Byte-by-byte Description of file: *.dat
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Bytes Format Units Label Explanations
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2- 5 I4 --- n Number of the line
6 A1 --- --- [:]
9- 10 I2 --- J' Upper state J quantum number
12- 13 I2 --- Ka' Upper state Ka quantum number
15- 16 I2 --- Kc' Upper state Kc quantum number
18- 19 I2 --- J'' Lower state J quantum number
21- 22 I2 --- Ka'' Lower state Ka quantum number
24- 25 I2 --- Kc'' Lower state Kc quantum number
46- 57 F12.5 MHz Freq-obs Observed transition frequency
60- 71 F12.5 MHz Freq-cal Calculated transition frequency
75- 82 F8.5 MHz O-C Observed minus calculated frequency
87- 93 F7.5 MHz e_Freq Experimental uncertainty
97-103 F7.5 --- --- [0]
106-117 F12.5 MHz Freq-cb ? Calculated frequency for blend
121-128 F8.5 MHz (O-C)-b ? Observed minus calculated frequency for blend
130-135 F6.4 --- w-b ? Weight of the components of the blend
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Acknowledgements:
Miguel Sanz Novo, miguel.sanz.novo(at)uva.es
(End) Miguel Sanz-Novo [GEM, UVa, Spain], Patricia Vannier [CDS] 10-Feb-2022