Far-Infrared detection of methylene

Abstract

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 N(CH2)=(7.5+/-1.1)x10^14 cm^-2. We compare this with the related molecule, CH, to determine [CH/CH2]=2.7+/-0.5. 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.

11 pages, 4 figures, accepted for publication in A&A

References in corpus (8)

• The far-IR spectrum of Sagittarius B2 region: Extended molecular absorption, photodissociation and photoionization
• Detection of interstellar CH_3
• Far-Infrared OH fluorescent emission in Sagittarius B2
• ISO-LWS observations of C+ and O lines in absorption toward SgrB2
• Water Absorption From Line-of-Sight Clouds Toward W49A
• Detection of HD in emission towards Sagittarius B2
• The line-of-sight distribution of water in the SgrB2 complex
• Far-infrared detection of 17OH towards Sagittarius B2

Cited by in corpus (14)

• Interstellar Hydrides
• Submillimeter absorption from SH+, a new widespread interstellar radical, 13CH+ and HCl
• First detection of the Methylidyne cation (CH+) fundamental rotational line with the Herschel/SPIRE FTS
• The ISO LWS high resolution spectral survey towards Sagittarius B2
• Sympathetic cooling of polyatomic molecules with S-state atoms in a magnetic trap
• Oxygen isotopic ratios in galactic clouds along the line of sight towards Sagittarius B2
• Herschel/HIFI Spectral Mapping of C${}^{+}$, CH${}^{+}$, and CH in Orion BN/KL: The Prevailing Role of Ultraviolet Irradiation in CH${}^{+}$ Formation
• Ground-state ammonia and water in absorption towards Sgr B2
• Herschel/HIFI observations of spectrally resolved methylidyne signatures toward the high-mass star-forming core NGC6334I
• PDRs4All. XII. FUV-driven formation of hydrocarbon radicals and their relation with PAHs
• Hunting for the elusive methylene radical
• Cold collisions of polyatomic molecular radicals with S-state atoms in a magnetic field: An ab initio study of He + CH2(X) collisions
• HyGAL: Characterizing the Galactic ISM with observations of hydrides and other small molecules II. The absorption line survey with the IRAM 30 m telescope
• Spectral survey of the diffuse gas toward BL Lac in the Q band