J/A+A/588/L8 Protonated formaldehyde in L1689B (Bacmann+, 2016)
Detection of protonated formaldehyde in the prestellar core L1689B.
Bacmann A., Garcia-Garcia E., Faure A.
<Astron. Astrophys. 588, L8 (2016)>
=2016A&A...588L...8B 2016A&A...588L...8B (SIMBAD/NED BibCode)
ADC_Keywords: Interstellar medium ; Spectroscopy
Keywords: ISM: molecules - line: identification - ISM: abundances
Abstract:
Complex organic molecules (COMs) are detected in many regions of the
interstellar medium, including prestellar cores. However, their
formation mechanisms in cold (∼10K) cores remain to this date poorly
understood. The formyl radical HCO is an important candidate precursor
for several O-bearing terrestrial COMs in cores, as an abundant
building block of many of these molecules. Several chemical routes
have been proposed to account for its formation, both on grain
surfaces, as an incompletely hydrogenated product of H addition to
frozen-out CO molecules, or in the gas phase, either the product of
the reaction between H2CO and a radical, or as a product of
dissociative recombination of protonated formaldehyde H2COH+. The
detection and abundance determination of H2COH+, if present, could
provide clues as to whether this latter scenario might apply. We
searched for protonated formaldehyde H2COH+ in the prestellar core
L1689B using the IRAM 30m telescope. The H2COH+ ion is
unambiguously detected, for the first time in a cold (∼10K) source.
The derived abundance agrees with a scenario in which the formation of
H2COH+ results from the protonation of formaldehyde. We use this
abundance value to constrain the branching ratio of the dissociative
recombination of H2COH+ towards the HCO channel to ∼10-30%. This value
could however be smaller if HCO can be efficiently formed from
gas-phase neutral- neutral reactions, and we stress the need for
laboratory measurements of the rate constants of these reactions at
10K. Given the experimental difficulties in measuring branching ratios
experimentally, observations can bring valuable constraints on these
values, and provide a useful input for chemical networks.
Description:
Line parameters for the 4 H2COH+ transitions observed in the
source L1689B. The frequency of the observed transition, the rms in
the spectrum, the peak main beam temperature, the linewidth, the error
on the linewidth, the line integrated intensity and the error on the
integrated line intensity are given. The peak main beam temperature,
linewidth and the integrated intensity were derived by Gaussian
fitting of the spectra. The corresponding reduced (folded and
baseline-subtracted) spectrum is given in antenna temperature units
Ta*.
Objects:
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RA (2000) DE Designation(s)
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16 34 42.1 -24 36 11 L1689B = LDN 1689B
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 71 4 Line parameters for H2COH+ transitions
sp/* . 4 Individual H2COH+ spectra
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See Also:
J/A+A/547/A33 : Chemical reactions for a deuteration network (Vastel+, 2012)
J/A+A/587/A130 : HCO and CH3O in prestellar cores (Bacmann+, 2016)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 9 F9.2 MHz Freq Frequency of the transition
13- 15 F3.1 mK rms rms noise in spectrum
19- 21 I3 mK Tmb ?=- Line peak intensity, Tmb
26- 29 F4.2 km/s dv ?=- Linewidth
33- 36 F4.2 km/s e_dv ?=- Error on linewidth
40 A1 --- l_Int Limit flag on intensity
41- 46 F6.4 K.km/s Int Integrated intensity
49- 54 F6.4 K.km/s e_Int ?=- Error on integrated intensity
58- 71 A14 --- FileName Name of corresponding spectrum file in
subdirectory sp
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Byte-by-byte Description of file: sp/*
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Bytes Format Units Label Explanations
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4- 13 F10.3 MHz Freq Frequency
19- 30 E12.5 K Int Intensity in Ta* unit
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Acknowledgements:
Aurore Bacmann, aurore.bacmann(at)univ-grenoble-alpes.fr
(End) Aurore Bacmann [IPAG], Patricia Vannier [CDS] 07-Mar-2016