DETECTION AND CHARACTERIZATION OF THE CUMULENE CARBENES H2C5 AND H2C6

Two cumulene carbenes, H2C5 and H2C6, were detected in a supersonic mo lecular beam by Fourier transform microwave spectroscopy. Their rotati onal and leading centrifugal distortion constants were determined with high accuracy, such that the entire radio spectrum can now be calcula ted. Like the known carbenes H2C2 and H2C4, both molecules have single t electronic ground states and linear carbon-chain backbones. They can be produced in sufficiently high concentrations in the laboratory tha t their electronic spectra, expected to lie in the visible, should be readily detectable by laser spectroscopy. The microwave spectra of oth er, more exotic isomers may be detectable as well.