15min:

C. A. GOTTLIEB, S. BRÜNKEN, M. C. MCCARTHY AND P. THADDEUS, Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, and Division of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138.

CN^- is a unique molecular anion because neutral CN has one of the highest known electron affinities, is observed under a wide range of terrestrial conditions, and because this closed-shell anion is structurally and spectroscopically quite simple, making it amenable to both laboratory detection and high-level quantum chemical calculations. Although CN^- has been studied by photoelectron spectroscopy, no high-resolution spectra have been reported. Here we report the laboratory rotational spectrum of CN^- observed in a low pressure glow discharge through C₂N₂ and N₂. Determination of the rotational and centrifugal distortion constants and the nitrogen quadrupole hyperfine coupling constant allow line frequencies to be calculated well into the far IR. CN^- is an excellent candidate for astronomical detection, because the CN radical is observed in many galactic molecular sources, and calculations indicate CN^- should be detectable in IRC+10216 --- the carbon star where C₆H^- has recently been observed. The fairly high concentration of CN^- in our discharge implies that other molecular anions containing the nitrile group may be within reach.