Laser-induced fluorescence detection of the elusive SiCF free radical

The SiCF free radical has been spectroscopically identified for the first time. The radical was produced in an electric discharge jet using CF₃Si(CH₃)₃ or CF₃SiH₃ vapor in high pressure argon as the precursor. The laser-induced fluorescence spectrum of the Ã∑+2-X̃∏2 band system in the 610 - 550 nm region was recorded and the ∏3/22 spin component of the 0-0 band was studied at high resolution. Rotational analysis gave the B values for the combining states, and by fixing the CF bond lengths at ab initio values we obtained r^″Si-C=1.6921Å and r^'Si-C=1.594(1)Å. The bond lengths correspond to a silicon-carbon double bond in the ground state and an unusual Si-C triple bond in the excited state. Single vibronic level emission spectra yielded the ground state bending and stretching energy levels. These were fitted to a Renner-Teller model that included spin-orbit and limited vibrational anharmonicity effects.