First detection of the C2 symmetric isomer of carbon pentaoxide (CO5) at 10 K

Carbon oxides of the form COn (n = 2–8) have long been known as important molecules in atmospheric and solid state chemical reactions. These higher order carbon oxides have been theoretically predicted to be stable, however, their detection has been difficult. Here, we report on the first spectroscopic detection of the cyclic (C2) isomer of carbon pentaoxide (12C16O5) via its ν1 vibrational mode centered around 1912 cm−1 under matrix isolation conditions; the identification of the 12C18O5, 13C16O5, and 13C18O5, isotopologues supported by ab initio calculations confirms the assignments. We also discuss possible formation routes of this molecule.