Letter to the Editor

Laboratory detection of the negative molecular ion CCH^-

¹ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA, and Division of Engineering and Applied Sciences, Harvard University, 29 Oxford Street, Cambridge, MA 02138, USA e-mail: sbruenken@cfa.harvard.edu
² Institute for Theoretical Chemistry, Department of Chemistry and Biochemistry, The University of Texas, Austin, TX 78712, USA

Received: 19 December 2006
Accepted: 19 January 2007

Abstract

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 millimeter-wave 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.