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Astron. Astrophys. 322, L1-L4 (1997)

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Letter to the Editor

Laboratory measurement of the [FORMULA] rotational transition of NH at 1 THz

Thomas Klaus , Shuro Takano and Gisbert Winnewisser

I. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, D-50937 Köln, Germany

Received 20 March 1997 / Accepted 4 April 1997


The [FORMULA] pure rotational transition of the NH radical ([FORMULA]), located at 1 THz, was measured with the Cologne terahertz spectrometer using a frequency stabilized backward wave oscillator as radiation source. The NH radical was produced in a dc discharge of a flowing mixture of ammonia and helium. Transition frequencies of all three fine structure transitions with associated hyperfine components were precisely measured and analyzed to determine accurate molecular constants, including hyperfine coupling constants for both nuclei. As a result, the accuracy of the molecular constants has been improved by one to two orders of magnitude. The nuclear spin-rotation coupling constant for the nitrogen nucleus has been determined for the first time. The precise frequencies reported in this work are of importance to astronomical applications.

Key words: Molecular data – Methods: laboratory – Techniques: spectroscopic – ISM: clouds – ISM: molecules

Send offprint requests to: klaus@ph1.uni-koeln.de


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© European Southern Observatory (ESO) 1997

Online publication: June 5, 1998