Spectroscopic identification and characterization of the aluminum methylene (AlCH₂) free radical

The AlCH₂ 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 B̃²A₂-X̃²B₁ band system in the 513-483 nm region was recorded, and the 0-0 bands of AlCH₂ and AlCD₂ 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 r^″A1-C=1.9591A◦,r^″C-H=1.1061A◦,θ_HCH ^″=110.41^◦ and r^'A1-C=1.9431A◦,r^'C-H=1.0911A◦,θ_HCH ^'=115.41^◦. The bond lengths correspond to an aluminum-carbon single bond in both states.