Gas phase synthesis of the C40 nano bowl C₄₀H₁₀

Nanobowls represent vital molecular building blocks of end-capped nanotubes and fullerenes detected in combustion systems and in deep space such as toward the planetary nebula TC-1, but their fundamental formation mechanisms have remained elusive. By merging molecular beam experiments with electronic structure calculations, we reveal a complex chain of reactions initiated through the gas-phase preparation of benzocorannulene (C₂₄H₁₂) via ring annulation of the corannulenyl radical (C₂₀H₉^•) by vinylacetylene (C₄H₄) as identified isomer-selectively in situ via photoionization efficiency curves and photoion mass-selected threshold photoelectron spectra. In silico studies provided compelling evidence that the benzannulation mechanism can be expanded to pentabenzocorannulene (C₄₀H₂₀) followed by successive cyclodehydrogenation to the C40 nanobowl (C₄₀H₁₀) - a fundamental building block of buckminsterfullerene (C₆₀). This high-temperature pathway opens up isomer-selective routes to nanobowls via resonantly stabilized free-radical intermediates and ring annulation in circumstellar envelopes of carbon stars and planetary nebulae as their descendants eventually altering our insights of the complex chemistry of carbon in our Galaxy.