Abstract
Using the Yebes 40m and IRAM 30m radio telescopes, we detected a series of harmonically related lines with a rotational constant B (0)=4460.590±0.001 MHz and a distortion constant D (0)=0.511 ±0.005 kHz towards the cold dense core TMC-1. High-level-of-theory ab initio calculations indicate that the best possible candidate is protonated tricarbon monoxide, HC(3)O(+). We have succeeded in producing this species in the laboratory and observed its J (u) -J (l) = 2-1 and 3-2 rotational transitions. Hence, we report the discovery of HC(3)O(+) in space based on our observations, theoretical calculations, and laboratory experiments. We derive an abundance ratio N(C(3)O)/N(HC(3)O(+))~7. The high abundance of the protonated form of C(3)O is due to the high proton affinity of the neutral species. The chemistry of O-bearing species is modelled, and predictions are compared to the derived abundances from our data for the most prominent O-bearing species in TMC-1.