| Issue |
A&A
Volume 431, Number 1, February III 2005
|
|
|---|---|---|
| Page(s) | 203 - 213 | |
| Section | Interstellar and circumstellar matter | |
| DOI | https://doi.org/10.1051/0004-6361:20041598 | |
| Published online | 02 February 2005 | |
Far-infrared detection of methylene *
1
Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany e-mail: epoleham@mpifr-bonn.mpg.de
2
Physikalisches Institut, Universität zu Köln, 50937 Cologne, Germany
3
Laboratoire d'Astrophysique de Marseille, CNRS & Université de Provence, BP 8, 13376 Marseille Cedex 12, France
Received:
5
July
2004
Accepted:
1
October
2004
We present a clear detection of CH2 in absorption towards the molecular cloud complexes Sagittarius B2 and W49 N using the ISO Long Wavelength Spectrometer. These observations represent the first detection of its low excitation rotational lines in the interstellar medium. Towards Sagittarius B2, we detect both ortho and para transitions allowing a determination of the total CH2 column density of 
cm-2. We compare this with the related molecule, CH, to determine [ CH/CH![$_{2}]=2.7\pm0.5$](/articles/aa/abs/2005/07/aa1598/aa1598_tex_eq2.png)
. Comparison with chemical models shows that the CH abundance along the line of sight is consistent with diffuse cloud conditions and that the high [ CH/CH2] ratio can be explained by including the effect of grain-surface reactions.
Key words: infrared: ISM / ISM: molecules / molecular data / ISM: individual objects: Sagittarius B2 / ISM: individual objects: W49
© ESO, 2005
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