A Comprehensive Spectral Rotational Analysis of the Interstellar Methyl Isocyanate CH₃NCO

Abstract

Methyl isocyanate (CH 3 NCO) is a recently identified interstellar molecule giving rise to many detected lines. Interestingly, its delayed identification was not due to weak lines but due to a very complex rotational spectrum. To date, the only published laboratory transitions for this molecule are those between rotational energy levels with K ≤ 3. In the present work, Stark modulation spectroscopy was used to record the room temperature rotational spectrum of CH 3 NCO in the spectral region from 32 to 90 GHz. Observation of characteristic Stark effects, measured at specific low-voltage modulation conditions, and 14 N nuclear quadrupole hyperfine structure allowed unambiguous assignment of rotational transitions up to K = 10. These newly assigned transitions were subsequently followed up to 364 GHz with the aid of Loomis-Wood-type displays. Since there are no reports on astrophysical detection of 13 C isotopic species, first laboratory measurements between 50 and 300 GHz have been also performed for CH 3 N 13 CO and 13 CH 3 NCO isotopologs. A comprehensive spectral analysis undertaken in this work made possible to extend the knowledge of the rotational spectrum of CH 3 NCO to more than 2500 new transitions. Furthermore, more than 1200 lines were identified and analyzed for each of the isotopologs. The extensive line lists and sets of molecular parameters reported in this work provide the basis for further astrophysical searches of CH 3 NCO.

Millimeter wave spectrum and search for vinyl isocyanate toward Sgr B2(N) with ALMA

“…Isocyanates are rather flexible molecules with many anomalies in their rotational spectra (Yamada 1980;Koput 1984;Cernicharo et al 2016;Pienkina et al 2017;Kolesniková et al 2018;Kolesniková et al 2019), and this has also proven to be the case for vinyl isocyanate. The ground-state rotational spectrum of the trans isomer suffers from strong perturbations which means that only transitions involving levels up to K a = 6 can be analyzed without the loss of physical meaning of the fitted constants.…”

Terahertz Spectroscopic Molecular Sensor for Rapid and Highly Specific Quantitative Analytical Gas Sensing

“…13,27 This approach is routinely used by astronomers to model molecular spectra in the interstellar medium. 12,28 To overcome library error in cases with excessive collisional broadening, a "model" of molecular absorption was developed. Figure 4 demonstrates the "model fit" to an acetaldehyde line recorded with the sensor.…”

Rotational spectroscopy of isotopic oxirane, $c$-C$_2$H$_4$O

“…Other recently studied isotopologs await detection in space. These include methylamine [22], methyl isocyanate [23], methyl mercaptan [24], and cyclopropenone [25].…”