The high-resolution LIF spectrum of the SiCCl free radical: Probing the silicon-carbon triple bond

Abstract

A rotationally resolved spectrum of a band of the A∼2Σ+ − X∼2Π electronic transition of the SiCCl free radical has been obtained for the first time. The radical was produced in an electric discharge jet using 1,1-dichlorosilacyclobutane vapor in high pressure argon as the precursor. The laser-induced fluorescence spectrum of the band system in the 610–550 nm region was recorded and the 2Π3/2 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 CCl bond lengths at ab initio values we obtained r″ (SiC) = 1.692(1) Å and r' (SiC) = 1.594(1) Å. The bond lengths correspond to a silicon-carbon double bond in the ground state and an unusual SiC triple bond in the excited state. Single vibronic level emission spectra yielded the ground state bending and stretching energy levels up to energies near 5000 cm−1. These were satisfactorily fitted to a Renner-Teller model that included spin–orbit and vibrational anharmonicity effects.