The (A) over tilde (2)A(1)-(X) over tilde E-2 electronic transition of the jet-cooled trichlorosiloxy (SiCl3O) free radical has been observed for the first time in the 650-590 nm region by laser induced fluorescence (LIF) detection. The radical was produced by a pulsed electric discharge through a mixture of silicon tetrachloride and oxygen in high pressure argon at the exit of a pulsed molecular beam valve. The LIF spectrum shows low frequency intervals, which we assign as activity in the normally forbidden degenerate v5 ' and v6 ' modes, indicative of a significant Jahn-Teller effect in the ground state. Single vibronic level emission spectra show level dependent spin-orbit splittings in the ground state and Jahn-Teller predictable variations depending on which upper state level is pumped. The measured lower state energy levels have been fitted to a Jahn-Teller model that simultaneously includes spin-orbit coupling and linear and quadratic multimode coupling. In SiCl3O, the Jahn-Teller interaction predominates over spin-orbit effects.
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