===== Formaldehyde in Space =====

L. E. Snyder, D. Buhl, B. Zuckerman, and P. Palmer\\
reported on the\\
**[[https://doi.org/10.1103/PhysRevLett.22.679|Microwave Detection of Interstellar Formaldehyde]]**\\
//Phys. Rev. Lett.// **22**, 679–681 (1969).\\
The 1<sub>1,0</sub> – 1<sub>1,1</sub> transition near 4830 MHz was detected in absorption with the 43 m NRAO telescope toward numerous continuum sources: M17, W3, W3(OH), W49, NGC 2024, DR 21, W43, W44, W51, Sgr A, Sgr B2, W33, NGC 6334, Cas A, and 3C 123. Formaldehyde was only the third poly-atomic molecule detected in space, the fourth molecule by radio astronomy, and the seventh molecule in space.

P. Palmer, B. Zuckerman, D. Buhl, and L. E. Snyder\\
studied\\
**[[https://ui.adsabs.harvard.edu/abs/1969ApJ...156L.147P|Formaldehyde Absorption in Dark Nebulae]]**\\
//Astrophys. J.// **156**, L147–L150 (1969).\\
The same transition was detected in several positions of Heiles' Cloud 2 with <sup>1</sup>H hyperfine structure resolved in part.

A. Heithausen, U. Mebold, and H. W. de Vries\\
performed\\
**[[https://ui.adsabs.harvard.edu/abs/1987A%26A...179..263H|A Survey of Formaldehyde in High Galactic Latitudes]]**\\
//Astron. Astrophys.// **179**, 263–267 (1987),\\
with the Effelsberg 100 m telescope which led to the detection of H<sub>2</sub>CO in translucent clouds.

A. G. Nash\\
studied\\
**[[https://ui.adsabs.harvard.edu/abs/1990ApJS...72..303N|The abundance ratio of formaldehyde to ammonia in molecular clouds observed toward radio continuum sources]]**\\
//Astrophys. J. Suppl. Ser.// **72**, 303–322 (1990),\\
which led to the detection of H<sub>2</sub>CO in diffuse clouds. The Effelsberg 100 m telescope and the 43 m NRAO dish were employed.

J. Cernicharo, M. Guélin, J. Penalver, J. Martín-Pintado, and R. Mauersberger\\
identified\\
**[[https://ui.adsabs.harvard.edu/abs/1989A%26A...222L...1C|A 200 km/s molecular outflow in the protoplanetary nebula CRL 618]]**\\
//Astron. Astrophys.// **222**, L1–L4 (1989)\\
in the course of a 3 and 1.3 mm line survey using the IRAM 30 m telescope. The C-rich PPN is also known as V353 Aur.

M. Lindqvist, H. Olofsson, A. Winnberg, and L.-Å. Nyman\\
investigated\\
**[[https://ui.adsabs.harvard.edu/abs/1992A%26A...263..183L|Carbon-bearing molecules in the envelopes around oxygen-rich stars – First detection of formaldehyde in an oxygen-rich circumstellar envelope]]**\\
//Astron. Astrophys.// **263**, 183–189 (1992).\\
The O-rich CSE was that of the PPN QX Pup, also known as OH231.8+4.2.

K. E. S. Ford, D. A. Neufeld, P. Schilke, and G. J. Melnick\\
reported on the\\
**[[https://doi.org/10.1086/423886|Detection of Formaldehyde toward the Extreme Carbon Star IRC+10216]]**\\
//Astrophys. J.// **614**, 990–1006 (2004).\\
The source, also known as CW Leo, is an asymptotic giant branch (AGB) star, which is the evolutionary phase prior to the PPN and PN phases.

L. Velilla Prieto, C. Sánchez Contreras, J. Cernicharo, M. Agúndez, G. Quintana-Lacaci, V. Bujarrabal, J. Alcolea, C. Balanca, F. Herpin, K. M. Menten, and F. Wyrowski\\
mentioned the detection of H<sub>2</sub>CO in the envelope of an O-rich AGB star in\\
**[[https://doi.org/10.1051/0004-6361/201628776|The millimeter IRAM-30 m line survey toward IK Tauri]]**\\
//Astron. Astrophys.// **597**, Art. No. A25 (2017).

Maser activity in formaldehyde was found by\\
D. Downes, T. L. Wilson\\
in their work on\\
**[[https://ui.adsabs.harvard.edu/abs/1974ApJ...191L..77D|Formaldehyde Line Emission at 4.8 GHz near NGC 7538]]**\\
//Astrophys. J.// **614**, L77–L78 (1974)\\
employing the Effelsberg 100 m telescope.

B. Zuckerman, P. Palmer, L. E. Snyder, and D. Buhl\\
reported on the\\
**[[https://ui.adsabs.harvard.edu/abs/1969ApJ...157L.167Z|Detection of Interstellar H<sub>2</sub><sup>13</sup>C<sup>16</sup>O]]**\\
//Astrophys. J.// **157**, L167–L171 (1969)\\
in Sgr B2, Sgr A, and possibly W51 using the NRAO 43 m telecope.

F. F. Gardner, J. C. Ribes, and B. F. C. Cooper\\
reported on the\\
**[[https://ui.adsabs.harvard.edu/abs/1971ApL.....9..181G|Detection of the <sup>18</sup>O Isotop(ologu)e of Formaldehyde at 4388 MHz]]**\\
//Astrophys. Lett.// **157**, 181–183 (1971)\\
in Sgr B2 using the Parkes 64 m telescope.

W. D. Langer, M. A. Frerking, R. A. Linke, and R. W. Wilson, reported on the\\
**[[https://ui.adsabs.harvard.edu/abs/1979ApJ...232L.169L|Detection of Deuterated Formaldehyde in Interstellar Clouds]]**\\
//Astrophys. J.// **157**, L167–L171 (1969).\\
The Bell Lab. 7 m telescope was used to detect the 2<sub>0,2</sub> – 1<sub>0,1</sub> transition near 128813 MHz in emission toward the dark clouds L134 N and Heiles' Cloud 2.

B. E. Turner\\
reported on the\\
**[[https://ui.adsabs.harvard.edu/abs/1990ApJ...362L..29T|Detection of doubly deuterated interstellar formaldehyde (D<sub>2</sub>CO) – an indicator of active grain surface chemistry]]**\\
//Astrophys. J.// **362**, L29–L33 (1990).\\
Four transition were detected in emission in the Compact Ridge of Orion KL using the NRAO 12 m telescope.

M. V. Persson, J. K. Jørgensen, H. S. P. Müller, A. Coutens, E. F. van Dishoeck, V. Taquet, H. Calcutt, M. H. D. van der Wiel, T. L. Bourke, and S. F. Wampfler\\
reported on the\\
**[[https://doi.org/10.1051/0004-6361/201731684|The ALMA-PILS Survey: Formaldehyde Deuteration in Warm Gas on Small Scales toward IRAS 16293–2422 B]]**\\
//Astron. Astrophys.// **610**, Art. No. A54 (2018).\\
They identified unambiguously H<sub>2</sub>C<sup>17</sup>O and D<sub>2</sub><sup>13</sup>CO; lines of HD<sup>13</sup>CO were too weak in that frequency range to be detected.


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Contributor(s): H. S. P. Müller; 01, 2017; 03, 2018

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