Laboratory rotational ground state transitions of NH${}_3$D${}^{+}$ and CF${}^{+}$

Abstract

Aims. This paper reports accurate laboratory frequencies of the rotational ground state transitions of two astronomically relevant molecular ions, NH3D+ and CF+. Methods. Spectra in the millimeter-wave band were recorded by the method of rotational state-selective attachment of He-atoms to the molecular ions stored and cooled in a cryogenic ion trap held at 4 K. The lowest rotational transition in the A state (ortho state) of NH${}_3$D${}^{+}$ ($J_K=1_0-0_0$), and the two hyperfine components of the ground state transition of CF${}^{+}$($J=1-0$) were measured with a relative precision better than $10^{-7}$. Results. For both target ions the experimental transition frequencies agree with recent observations of the same lines in different astronomical environments. In the case of NH${}_3$D${}^{+}$ the high-accuracy laboratory measurements lend support to its tentative identification in the interstellar medium. For CF${}^{+}$ the experimentally determined hyperfine splitting confirms previous quantum-chemical calculations and the intrinsic spectroscopic nature of a double-peaked line profile observed in the $J=1-0$ transition towards the Horsehead PDR.

7 pages, 2 figures

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• The complexity of Orion: an ALMA view III. The explosion impact