Free access article

A&A 428, 117-120 (2004)
DOI: 10.1051/0004-6361:20041649

The abundance of in diffuse clouds

H. Liszt¹, R. Lucas² and J. H. Black<sup>3

1</sup>  National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903-2475, USA
    e-mail: hliszt@nrao.edu
²  Institut de Radioastronomie Millimétrique, 300 rue de la Piscine, 38406 Saint-Martin-d'Hères, France
³  Chalmers Centre for Astrophysics and Space Science, Onsala Space Observatory, Chalmers University of Technology, 43992 Onsala, Sweden

(Received 12 July 2004 / Accepted 23 August 2004)

Abstract
We used the Plateau de Bure Interferometer to search for 3mm absorption lines of HOC ⁺ from local diffuse and translucent clouds occulting compact extragalactic mm-wave continuum sources. We detected HOC ⁺ in three directions with column densities only 70-120 times below that of the HCO ⁺ isomer, a factor 5-50 higher than typically found in dense dark gas but comparable to recent observations of dense photon-dominated regions. The observed amounts of HOC ⁺ N(HOC ⁺)/ N(H ₂)  can be made in quiescent diffuse gas at thermal gas-kinetic rates if the H ₂O/OH ratio is of order unity, in mild violation of extant observational limits.

Key words: ISM: molecules -- astrochemistry

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© ESO 2004

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