Linear and cyclic propanylidene (C3H2) are known interstellar molecules, but their full rovibrational features have yet to be fully established. The present high-level quantum chemical analysis performed in this work provides the symmetric hydride bends to within 2.0 cm-1 and the rotational constants to within 30 MHz of gas phase experiment. Subsequently, the search for possible, natural, noble gas molecules has led to quantum chemical, spectroscopic analysis of NeCCH+, ArNH+, ArCCH+, ArCN+. Each of these systems has been previously shown to be a stable minimum on its respective potential energy surface. However, no spectroscopic data are available for laboratory detection or interstellar observation of these species, and the interstellar medium may be the most likely place in nature where the noble gas cations are found. The bent shape of NeCCH+ is confirmed here with a fairly large dipole moment and a bright C−H stretching frequency at 3101.9 cm−1. Even if this molecule is somewhat unstable, it is likely observable now that the spectral ranges of where to look have been established. ArCCH+ is much more stable but has dim double harmonic intensities for the vibrational fundamentals and a dipole moment below 0.5 D making its rotational transitions likely buried in the astronomical weeds. Even so, ArCCH+ cannot be excluded as a possibility in laboratory experiments of hydrocarbons in argon-rich environments. ArCN+, on the other hand, has a dipole moment of greater than 3.5 D, an observable C−N stretching fundamental at 2189.6 cm−1, and a viable formation pathway through HCN, a highly-abundant interstellar molecule. Consequently, the molecules containing noble gas atoms are spectroscopically classified at high-level for the first time and may be present in observable regions of outer space.

Rovibrational spectra of potential interstellar noble gas molecules and small hydrocarbons

254th National Meeting (2017)

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