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

Laser-induced fluorescence and wavelength resolved emission spectra of the (C) over tilde B-2(2)-(X) over tilde (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 AlC2 have been determined in both the combining states along with several of the anharmonicity constants. The theta(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) angstrom, r ''(0) (Al-C) = 1.926(1) angstrom, theta ''(C-Al-C) = 38.5(2)degrees, r'(0)(C-C) = 1.323(2) angstrom, r'(0)(Al-C) = 1.934(1) angstrom, and theta'(C-Al-C) = 40.0(2)degrees. Unlike SiC2, aluminum dicarbide shows no spectroscopic evidence of facile isomerization to the linear structure in the ground electronic state. (C) 2011 American Institute of Physics. [doi:10.1063/1.3638049]