Rotational spectroscopy of rare iron monoxide isotopologues: A mass-independent analysis

Abstract

We present pure rotational transitions of the rare iron monoxide isotopologues. ${}^{57}\mathrm{F}{\mathrm{e}}^{16}\mathrm{O}$, ${}^{58}\mathrm{F}{\mathrm{e}}^{16}\mathrm{O}$ and ${}^{56}\mathrm{F}{\mathrm{e}}^{18}\mathrm{O}$ in their lowest spin states ${}^5{\mathrm{\Delta }}_4$. For ${}^{57}\mathrm{F}{\mathrm{e}}^{16}\mathrm{O}$, the rotational spectrum reveals hyperfine splitting due to the nuclear spin of $I({}^{57}\mathrm{Fe})=1/2$. We use Dunham-like parameters to analyse the new laboratory data together with data from the literature. In particular, we are able to derive the Born–Oppenheimer breakdown parameters ${\mathrm{\Delta }}_{U01}^{\mathrm{Fe}}=-9.886(24)$ and ${\mathrm{\Delta }}_{U01}^{\mathrm{O}}=-10.761(67)$ and the corresponding equilibrium bond length of $r_e^{\mathrm{BO}}=1.6160302(20){10}^{-10}\mathrm{m}$. With these new accurate molecular parameters line positions on a sub-MHz accuracy level can be calculated, including those of the radioactive isotopologue ${}^{60}\mathrm{F}{\mathrm{e}}^{16}\mathrm{O}$. The new data allow for an astronomical search for the rare $\mathrm{FeO}$ isotopologues using sensitive radio telescopes, like the Atacama Large Millimetre/submillimetre Array.

GRAPHICAL ABSTRACT

Keywords:

• FeO
• mm-wave
• radioactive molecule
• supersonic jet expansion
• Dunham

Acknowledgments

T.F.G. and co-workers would like to express their gratitude for 30 years of collaboration with Jürgen Gauss in the analysis of new molecules.

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes

1 Allen et al.  [25] measured absorption signals using a double pass optics through a Broida-type oven at static conditions. In this configuration, only symmetric Doppler components are expected as have been seen. In contrast, our absorption signals were measured in perpendicular orientation to the supersonic jet expansion. Deviation from perpendicular configuration may result in a shift of the centre frequency due to asymmetric Doppler components. However, a comparison of both datasets shows, that our lines match within a $1\sigma$ standard deviation and we concluded that the supersonic jet was perfectly aligned.

Additional information

Funding

DFG priority program 1573 (Physics of the Interstellar Medium) under grant numbers GI 319/3-1, GI 319/3-2, the University of Kassel ‘Programmlinie Zukunft’, through P/1052 and funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – Projektnummer 328961117 – SFB 1319 ELCH.