J/A+A/670/A177 Doubly deuterated acetaldehyde (Ferrer Asensio+, 2023)
Millimetre and sub-millimetre spectroscopy of doubly deuterated acetaldehyde
(CHD2CHO) and first detection towards IRAS 16293-2422.
Ferrer Asensio J., Spezzano S., Coudert L.H., Lattanzi V., Endres C.P.,
Jorgensen J.K., Caselli P.
<Astron. Astrophys. 670, A177 (2023)>
=2023A&A...670A.177F 2023A&A...670A.177F (SIMBAD/NED BibCode)
ADC_Keywords: Atomic physics
Keyword: ISM: molecules - ISM: clouds - ISM: abundances - radio lines: ISM -
stars: formation - radiative transfer - line: identification
Abstract:
The abundances of deuterated molecules with respect to their main
isotopologue counterparts have been determined to be orders of
magnitude higher than expected from the cosmic abundance of deuterium
relative to hydrogen. The increasing number of singly and
multi-deuterated species detections helps us to constrain the
interplay between gas-phase and solid-state chemistry and to
understand better deuterium fractionation in the early stages of star
formation. Acetaldehyde is one of the most abundant complex organic
molecules (COMs) in star-forming regions and its singly deuterated
isotopologues have already been observed towards protostars. A
spectroscopic catalogue for astrophysical purposes is built for doubly
deuterated acetaldehyde (CHD2CHO) from measurements in the
laboratory. With this accurate catalogue we aim to search and detect
this species in the interstellar medium and retrieve its column
density and abundance. Submillimetre wave transitions were measured
for the non-rigid doubly deuterated acetaldehyde CHD2CHO displaying
hindered internal rotation of its asymmetrical CHD2 methyl group. An
analysis of a dataset consisting of previously measured microwave
transitions and of the newly measured ones was carried out with an
effective Hamiltonian which accounts for the tunneling of the
asymmetrical methyl group. A line position analysis is carried out
allowing us to reproduce 853 transition frequencies with a weighted
root mean square standard deviation of 1.7, varying 40 spectroscopic
constants. A spectroscopic catalogue for astrophysical purposes is
built from the analysis results. Using this catalogue we were able to
detect for the first time CHD2CHO towards the low-mass protostellar
system IRAS 16293-2422 utilizing data from the ALMA Protostellar
Interferometric Line Survey. The first detection of the CHD2CHO
species allows for the derivation of its column density with a value
of 1.3x1015cm-2 and an uncertainty of 10-20%. The resulting
D2/D ratio of ∼20% is found to be coincident with D2/D ratios
derived for other complex organic molecules towards IRAS 16293-2422,
pointing at a common formation environment with enhanced deuterium
fractionation.
Description:
Two complementary tables are presented.
Table 3 lists the assignments, observed and calculated frequencies,
and residuals of the CHD2CHO lines measured in this work as well as
past manuscripts.
Table 6 corresponds to the spectroscopic catalogue, formatted as the
catalogue files from the JPL database, build from the fitting of the
CHD2CHO measured transitions.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table3.dat 67 1013 Line assignments
table6.dat 75 8679 CHD2CHO spectroscopic catalogue
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
2- 3 I2 --- Ju Quantum number J of the upper state
5- 6 I2 --- Kau Quantum number Ka of the upper state
8- 9 I2 --- Kcu Quantum number Kc of the upper state
11 A1 --- vu [±2] Vibrational quantum number of
the upper state (1)
15- 16 I2 --- J Quantum number J of the lower state
18- 19 I2 --- Ka Quantum number Ka of the lower state
21- 22 I2 --- Kc Quantum number Kc of the lower state
24 A1 --- v [±2] Vibrational quantum number of
the lower state (1)
27- 36 F10.3 MHz Freq Line frequency observed
39- 40 I2 MHz e_Freq Line frequency uncertainty
44- 47 I4 MHz O-C Frequency difference (obs - calc)
48 A1 --- n_O-C [d] Note on O-C
50- 67 A18 --- Ref Reference (2)
--------------------------------------------------------------------------------
Note (1): Vibrational quantum number as follows:
+ = rotational level arising from the + tunneling sublevel
- = rotational level arising from the - tunneling sublevel
2 = those arising from the In configuration
Note (2): References:
Turner & Cox 1976, Chemical Physics Letters, 42, 84
Turner et al. 1981, J. Chem. Soc., Faraday Trans. 2,77, 1217
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table6.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
3- 13 F11.4 MHz Freq Transition frequency
15- 21 F7.4 MHz e_Freq Transition frequency error
23- 29 F7.4 [nm+2.MHz] logInt Base 10 logarithm of the line intensity
31 I1 --- DF [3] Degrees of freedom of Q(rot)
33- 41 F9.4 cm-1 Elow Lower state energy
43- 44 I2 --- Gup Upper state degeneracy
46- 61 A16 --- Tag Species tag
63 I1 --- QN [0/2] Format number
68- 73 A6 --- QNup Upper state quantum numbers
75 I1 --- QNlow [0/2] Lower state quantum numbers
--------------------------------------------------------------------------------
Acknowledgements:
Judit Ferrer Asensio, ferrer(at)mpe.mpg.de
(End) Patricia Vannier [CDS] 19-Jan-2023