Doppler-limited rotational spectrum of the NH radical in the 2 THz region |
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Authors: | Frank Lewen Gisbert Winnewisser Štěpán Urban |
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Institution: | a I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, D-50937 Cologne, Germany b The J. Heyrovsky Institute of Academy of Sciences, Dolejškova 3, CZ-18223 Prague, 8, Czech Republic c Department of Analytical Chemistry, Institute of Chemical Technology, Technická 5, 166 28 Prague 6, Czech Republic |
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Abstract: | The Doppler-limited rotational spectrum of the NH radical in its electronic (X) and vibrational ground state has been measured using the frequency stabilized Cologne side-band spectrometer in the frequency region near 2 THz. The nitrogen 14N nuclear hyperfine patterns have been observed accompanying the resolved fine (J′←J″) structure of the N=2←1 rotational transition. The observed peak frequencies were analyzed in detail together with the previously measured hyperfine frequencies of the N=1←0 rotational transition and with combination differences obtained from the high-resolution electronic spectra to derive precise rotational, centrifugal distortion, fine, and hyperfine parameters. In the numerical analysis the essential attention has been paid to partly resolved and unresolved hyperfine structures. The peak positions of the partly or fully overlapped lines were analyzed with the help of a profile simulation with estimated half-widths and calculated relative intensities and in this manner the least square fit of the unresolved and partly resolved lines was significantly improved. The NH radical is an extremely important species in nitrogen chemical reaction networks in the interstellar medium and atmospheric chemistry. |
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Keywords: | Radical NH High-resolution molecular spectra Fine structure Hyperfine structure of rotational levels Rotational spectra NH Theory of fine and hyperfine structures Atmospheric molecular species Molecular astrophysics |
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