The rotational spectrum and angular geometry of a pre-reactive complex of allene and chlorine monofluoride

Ground-state rotational constants, centrifugal distortion constants and Cl nuclear quadrupole coupling constants were determined from the rotational spectra of two isotopomers (allene⋯35ClF and allene⋯37ClF) of a pre-reactive complex of allene and chlorine monofluoride. Chemical reaction between the components was avoided by using a fast-mixing nozzle in a Fourier transform microwave spectrometer. It is concluded that the observed complex is of the weakly bound, Mulliken outer type in which the Cl of ClF interacts with the π-bond of allene to give an L-shaped geometry with the heavy atoms coplanar.