Abstract
We report first laboratory rest frequencies for rotational transitions of protonated methylamine, CH3NH3+, measured in a cryogenic 22-pole ion trap machine and employing an action spectroscopy scheme. For this prolate symmetric top molecule thirteen transitions between 80 and 240 GHz were detected in the ground vibrational state, covering JK = 2K − 1K up to JK = 6K − 5K with K = 0, 1, 2. Some transitions exhibit noticeable structure that is attributed to internal rotation splitting. As the CN radical and several of its hydrogenated and protonated forms up to methylamine, CH3NH2, are well known entities in the laboratory and in space, protonated methylamine, CH3NH3+, is a promising candidate for future radio astronomical detection.
Highlights
The cyano radical, CN, was one of the first molecules detected in the interstellar medium (McKellar, 1940)
Following up on our recent work on the high-resolution rotational spectra of CN+ (Thorwirth et al, 2019a) and CH2NH+2 (Markus et al, 2019), in this study, we focus on the very last member of the CN hydrogenation/protonation chain, protonated methylamine, CH3NH3+
This deep integration was necessary due to the comparably small signal strength, and due to somewhat noisy signal counts, which had its origin in ion source instabilities caused by the sticky consistency of the methylamine precursor
Summary
The cyano radical, CN, was one of the first molecules detected in the interstellar medium (McKellar, 1940). Examples are CH3NH3+, as a product of proton transfer to methyl amine (see, e.g., the KIDA database; Wakelam et al, 2015) or from radiative association of NH3 and CH3+ (Herbst, 1985), and protonated methanol, CH3OH+2 (Jusko et al, 2019), and protonated methane, CH+5 (Asvany et al, 2012; Asvany et al, 2015). In particular the latter two molecular ions have not yet been searched for in space because their laboratory microwave spectra are predicted to be quite irregular and still not known
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