THE ROTATIONAL SPECTRUM OF CN$^-$
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Publisher:Ohio State University
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,}, 800 (1993).} no high-resolution spectra have been reported. Here we report the laboratory rotational spectrum of CN$^-$ observed in a low pressure glow discharge through C$_2$N$_2$ and N$_2$. 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}, 137 (1996).} indicate CN$^-$ should be detectable in IRC+10216 --- the carbon star where C$_6$H$^-$ 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.
Author Institution: Harvard-Smithsonian Center for Astrophysics, 60 Garden Street,; Cambridge, MA 02138, and Division of Engineering; and Applied Sciences, Harvard University, Cambridge, MA 02138
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