The rotational spectrum and structure of a weakly bound complex of ketene and acetylene

An improvised pulsed-nozzle Fourier-transform microwave spectrometer was used to explore the ketene-acetylene CH2CO-C2H2 complex. The hydrogen nucleus of ketene and acetylene are exchanged by tunneling motions, and this is revealed by relative intensity estimations. The complex preserved a planar structure that is unlike the crossed configuration normally associated with a (2-pi(s) + 2-pi(a)) cycloaddition reaction.