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Description
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, CH_3_CO^+^, 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 CH_3_CO^+^ in space based on our observations, theoretical calculations, and laboratory experiments. The derived rotational and distortion constants allow us to predict the spectrum of CH_3_CO^+^ with high accuracy up to 500GHz. We derive an abundance ratio N(H_2_CCO)/N(CH_3_CO^+^)~44. The high abundance of the protonated form of H2CCO is due to the high proton affinity of the neutral species. The other isomer, H_2_CCOH^+^, is found to be 178.9kJ/mol above CH_3_CO^+^. 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 H_2_, or during their formation through the reaction of H_3_^+^ with H_2_CCO.
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