The rotational spectrum and structure of HOOOH

Hydrogen oxides, H2On with n) 1 (i.e., water) and n) 2 (i.e., hydrogen peroxide), are familiar species in various fields of natural science. However, extended species (n> 2), namely, hydrogen polyoxides, have been believed to be quite unstable due to the repulsion between the lone-pair electrons on the oxygen atoms. Thus, the questions, “how long can you make an oxygen chain?1” and “if such oxygen chain molecules exist, what kind of roles do these molecules play? ” have long been fascinating chemists even from the19th century.2 Recently, we have reported a microwave observation of a radical species with three oxygen atoms, HO3, and determined its precise molecular structure. HO3 is regarded as a weak adduct of HO-O2 and is expected to be a sink of the atmospheric OH radical.3 On the other hand, no detection of a closed shell species, H2O3, in the gas phase has been reported yet. Its existence and stability in the gas phase, as well as its precis