Detection and Characterization of the Cumulene Carbenes H 2 C 5 and H 2 C 6

Abstract

Two cumulene carbenes, H ₂ C ₅ and H ₂ C ₆ , were detected in a supersonic molecular beam by Fourier transform microwave spectroscopy. Their rotational and leading centrifugal distortion constants were determined with high accuracy, such that the entire radio spectrum can now be calculated. Like the known carbenes H ₂ C ₃ and H ₂ C ₄ , both molecules have singlet electronic ground states and linear carbon-chain backbones. They can be produced in sufficiently high concentrations in the laboratory that their electronic spectra, expected to lie in the visible, should be readily detectable by laser spectroscopy. The microwave spectra of other, more exotic isomers may be detectable as well.