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, 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 J(u) = 10 up to J(u) = 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 500 GHz. We derive an abundance ratio N(H(2)CCO)/N(CH(3)CO(+))~44. The high abundance of the protonated form of H(2)CCO is due to the high proton affinity of the neutral species. The other isomer, H(2)CCOH(+), is found to be 178.9 kJ mol(-1) 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 H3+ with H(2)CCO.