Further analysis of the laboratory rotational spectrum of CH3NCO

Abstract

Identification by the Rosetta mission that CH$_3$NCO is among the more plentiful molecules on the surface of the comet Churyumov-Gerasimenko stimulated rapid detection of this molecule in the interstellar medium.\footnote{D.T.Halfen, V.V.Ilyushin, L.Ziurys, {\it ApJ} {\bf 812}, L5 (1915).}$^,$\footnote{J.Cernicharo, Z.Kisiel, B.Tercero, et al., {\it A\&A} {\bf 587}, L4 (2016).} In particular, we have been successful in detecting almost 400 lines of CH$_3$NCO in Orion$^b$ by extending the Koput\footnote{J.Koput, {\it J.~Mol.~Spectrosc.} {\bf 115}, 131 (1986).} cm-wave assignment to frequencies relevant to mm-wave radio-telescopes through measurement of the complete laboratory spectrum up to 363 GHz.$^{b,}$\footnote{Z.Kisiel et al., 65$^{th}$ ISMS, Columbus, Ohio, RC-13 (2010)

\, 70$^{th}$ ISMS, Champaign-Urbana, Illinois, TG-08 (2015).}

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Presently, we describe further progress in understanding the laboratory rotational spectrum of CH$_3$NCO. Assignment has been extended to transitions with $K>3$ by analysis of Stark and hyperfine patterns of the corresponding lowest-$J$ transitions. Broadband spectra of synthezised pure $^{13}$CH$_3$NCO and CH$_3$N$^{13}$CO isotopic species have also been recorded and assigned. Furthermore, the progress in fitting this very low barrier and highly perturbed internal rotation spectrum is described.