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Updated: Apr 23, 2026

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Published on: July 27, 2018
The rotational spectrum of CN-
C A Gottlieb1, S Brünken, M C McCarthy
1Harvard-Smithsonian Center for Astrophysics, Division of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA.
The rotational spectrum of the molecular negative ion cyanogen (CN-) was detected in a laboratory setting. This finding suggests CN- is a strong candidate for astronomical detection in space.
Area of Science:
- * Molecular Spectroscopy
- * Astrochemistry
- * Quantum Chemistry
Background:
- * The molecular negative ion cyanogen (CN-) has been theorized to exist in interstellar environments.
- * Previous studies have focused on the neutral cyanogen radical (CN), but the negative ion (CN-) remained experimentally uncharacterized.
- * The detection of molecular anions is crucial for understanding interstellar chemistry and the formation of complex molecules.
Purpose of the Study:
- * To experimentally detect and characterize the rotational spectrum of the molecular negative ion CN-.
- * To provide spectroscopic constants for accurate astronomical predictions.
- * To assess the potential for astronomical detection of CN- in interstellar clouds.
Main Methods:
- * High-resolution rotational spectroscopy was employed.
- * Experiments were conducted using a low-pressure glow discharge in a mixture of cyanogen (C2N2) and nitrogen (N2).
- * Nitrogen quadrupole hyperfine structure and Doppler shifts were analyzed for conclusive identification.
Main Results:
- * The four lowest rotational transitions of CN- were successfully observed and measured.
- * Spectroscopic constants (B, D, and eQq) were determined with high accuracy (better than 1 part in 10^7).
- * The observed spectrum allows for precise calculation of the rotational spectrum well into the far-infrared region.
Conclusions:
- * The molecular negative ion CN- has been definitively identified through its rotational spectrum.
- * CN- is an excellent candidate for astronomical detection, particularly in carbon-rich environments like IRC+10216.
- * The successful detection implies that other nitrile-containing molecular anions may also be detectable with current laboratory techniques.
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