Discovery of the acetyl cation, CH3CO+, in space and in the laboratory

TL;DR

This study reports the first detection of the acetyl cation, CH3CO+, in space, supported by astronomical observations, laboratory synthesis, and theoretical calculations, revealing its spectral properties and abundance in cold dense cores.

Contribution

The paper provides the first identification of CH3CO+ in space, combining observational, experimental, and theoretical methods to characterize its spectrum and abundance.

Findings

Detection of CH3CO+ lines in multiple space sources.

Laboratory measurement of rotational transitions of CH3CO+.

Theoretical calculations confirm the candidate as the acetyl cation.

Abstract

Using the Yebes 40m and IRAM 30m radiotelescopes, we detected two series of harmonically related lines in space that can be fitted to a symmetric rotor. The lines have been seen towards the cold dense cores TMC-1, L483, L1527, and L1544. High level of theory ab initio calculations indicate that the best possible candidate is the acetyl cation, CH3CO+, which is the most stable product resulting from the protonation of ketene. We have produced this species in the laboratory and observed its rotational transitions Ju = 10 up to Ju = 27. Hence, we report the discovery of CH3CO+ in space based on our observations, theoretical calculations, and laboratory experiments. The derived rotational and distortion constants allow us to predict the spectrum of CH3CO+ with high accuracy up to 500 GHz. We derive an abundance ratio N(H2CCO)/N(CH3CO+) = 44. The high abundance of the protonated form of H2CCO is due to the high proton affinity of the neutral species. The other isomer, H2CCOH+, is found to be 178.9 kJ/mol above CH3CO+. The observed intensity ratio between the K=0 and K=1 lines, 2.2, strongly suggests that the A and E symmetry states have suffered interconversion processes due to collisions with H and/or H2, or during their formation through the reaction of H3+ with H2CCO.