Pulsed discharge jet electronic spectroscopy of the aluminum dicarbide (AlC2) free radical.

Laser-induced fluorescence and wavelength resolved emission spectra of the C 2B2-X 2A1 band system of the gas phase aluminum dicarbide free radical have been obtained using the pulsed discharge jet technique. The radical was produced by electron bombardment of a precursor mixture of trimethylaluminum in high-pressure argon. The three vibrational frequencies of T-shaped AlC2 have been determined in both the combining states along with several of the anharmonicity constants. The 0₀⁰ band has been recorded with high resolution and rotationally analyzed. The spectrum is complicated by partially resolved spin-rotation and aluminum hyperfine splittings. Where necessary, we have fixed the spin-rotation constants used in the rotational analysis at the values predicted by density functional theory. The derived molecular structures are: r₀^′′(C-C) = 1.271(2) Å, r₀^′′(Al-C) = 1.926(1) Å, θ″(C-Al-C) = 38.5(2)°, r₀^′(C-C) = 1.323(2) Å, r₀^′(Al-C) = 1.934(1) Å, and θ′(C-Al-C) = 40.0(2)°. Unlike SiC2, aluminum dicarbide shows no spectroscopic evidence of facile isomerization to the linear structure in the ground electronic state. [ABSTRACT FROM AUTHOR]