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

Laser-induced fluorescence and wavelength resolved emission spectra of the C ̃(2)B(2)-X̃ (2)A(1) 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 AlC(2) have been determined in both the combining states along with several of the anharmonicity constants. The 0(0)(0) 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: r(0)('')(C-C) = 1.271(2) Å, r(0)('')(Al-C) = 1.926(1) Å, θ(")(C-Al-C) = 38.5(2)°, r(0)(')(C-C) = 1.323(2) Å, r(0)(')(Al-C) = 1.934(1) Å, and θ(')(C-Al-C) = 40.0(2)°. Unlike SiC(2), aluminum dicarbide shows no spectroscopic evidence of facile isomerization to the linear structure in the ground electronic state.