Laboratory detection of the negative molecular ion CCH-

Aims. This paper reports the laboratory detection of the rotational spectrum of the acetylide anion, CCH-. Methods. Five successive rotational transitions have been measured to high accuracy in a dc discharge with a free space millimeterwave spectrometer in the frequency range 83 - 417 GHz. Results. Precise spectroscopic constants have been obtained for CCH- and transition rest frequencies can now be calculated to better than 1 km s(-1) in equivalent radial velocity far into the terahertz region, allowing for deep astronomical searches for this anion in space. The highly stable and fairly polar CCH- anion is a likely candidate for radio astronomical detection, its neutral analogue CCH being among one of the most abundant molecules in a wide variety of astrophysical sources.