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 Title: Measurement Of The Lowest Millimeter-wave Transition Frequency Of The Ch Radical Author(s): Truppe, Stefan Contributor(s): Tarbutt, Michael; Hinds, Ed; Hendricks, Richard James Subject(s): Mini-symposium: Astronomical Molecular Spectroscopy in the Age of ALMA Abstract: The CH radical is an important constituent of stellar atmospheres, interstellar gas clouds and is of fundamental importance to interstellar chemistry. Furthermore, it offers a sensitive way to test the hypothesis that fundamental constants measured on earth may differ from those observed in other parts of the universe\footnote{S. Truppe et al., \textit{Nature Communications}~\underline{\textbf{4}}, 2600, 2013}. Here, we present a measurement of the lowest millimeter-wave transition of CH, near 535~GHz, with an accuracy of 0.6~kHz\footnote{S. Truppe et al., \textit{The Astrophysical Journal}~\underline{\textbf{780}}, 71, 2014}, an improvement of nearly two orders of magnitude compared to the previous best rest frequencies. We drive the millimeter-wave transitions using the 54th harmonic of a frequency synthesizer phase-locked to a 10 MHz GPS frequency reference. Using ALMA this transition has recently been observed in the absorber PKS 1830-211 at a redshift of $z=0.89$\footnote{S. Muller, \textit{private communication}, 2013}. As pointed out by de Nijs et al.\footnote{de Nijs et al., \textit{Physical Review A}~\underline{\textbf{86}}, 032501, 2012} a very robust and sensitive means to search for variations in fundamental constants could be obtained by observing the lowest millimeter-wave transition of CH along with the two $\Lambda$-doublets at 3.3 and 0.7~GHz, all from the same interstellar gas cloud. Issue Date: 2014-06-18 Publisher: International Symposium on Molecular Spectroscopy Citation Info: Truppe, S.; Tarbutt, M.; Hinds, E.; Hendricks, R.J. MEASUREMENT OF THE LOWEST MILLIMETER-WAVE TRANSITION FREQUENCY OF THE CH RADICAL. Proceedings of the International Symposium on Molecular Spectroscopy, Urbana, IL, June 16-21, 2014. DOI: 10.15278/isms.2014.WF05 Genre: CONFERENCE PAPER/PRESENTATION Type: Text Language: English URI: http://hdl.handle.net/2142/51054 DOI: 10.15278/isms.2014.WF05 Rights Information: Copyright 2014 by the authors. Licensed under a Creative Commons Attribution 4.0 International License. http://creativecommons.org/licenses/by/4.0/ Date Available in IDEALS: 2014-09-172015-04-14
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