Spectroscopic identification and characterization of the aluminum methylene (AlCH) free radical.

The AlCH free radical has been spectroscopically identified for the first time. This highly reactive species was produced in an electric discharge jet using trimethylaluminum vapor in high pressure argon as the precursor. The laser-induced fluorescence spectrum of the B̃A-X̃B band system in the 513-483 nm region was recorded, and the 0-0 bands of AlCH and AlCD were studied at high resolution. The fine structure splittings were found to be due primarily to the Fermi contact interaction in the excited state rather than the usual spin-rotation coupling. Rotational analysis gave the molecular constants of the combining states, and the geometries were obtained as rA1-C=1.9591A◦,rC-H=1.1061A◦,θ =110.41 and rA1-C=1.9431A◦,rC-H=1.0911A◦,θ =115.41. The bond lengths correspond to an aluminum-carbon single bond in both states.