Microwave spectrum of FeCl radical in the electronic ground 6Δi state

The rotational spectrum of the FeCl radical in the electronic ground state was observed by using a source-modulated millimeter-wave spectrometer. This species was produced in a free-space cell by glow-discharging a mixture of helium and aluminum trichloride vapor. Iron atoms were extracted during the discharge from the stainless-steel electrodes in the cell. The spectrum was observed for the two lowest-lying spin components of the inverted sextet Δ state. The rotational and centrifugal distortion constants were determined by a least-squares fit to the line frequencies of each spin substate.