FOURIER TRANSFORM EMISSION SPECTROSCOPY OF THE $g^{4} \Delta - a^{4} \Delta$ SYSTEM OF FeCl

Author Institution: Department of Chemistry, University of Arizona; Department of Chemistry, University of WaterlooThe emission spectrum of FeCl has been investigated at high resolution in the near infrared. The molecule was excited in a microwave discharge lamp using a mixture of FeCl3 vapor and 2.5 Torr of He, and the spectra were recorded in the $3000-12500 cm^{-1}$ region using a Fourier transform spectrometer. New bands with R heads near 7725, 8149, 8577, 8949, 9319, 9686 and $10050 cm^{-1}$ have been assigned as the $0-2, 0-1, 0-0, 1-0, 2-0, 3-0$ and $4-0$ bands of a new $g^{4}\Delta - a^{4}\Delta$ system of FeCl. The strong bands of this system consist of four subbands assigned as $^{4}\Delta_{1/2^{-}}^{4}\Delta_{1/2}$, $^{4}\Delta_{3/2^{-}}^{4} \Delta_{3/2,}^{4} \Delta_{5/2^{-}}^{4} \Delta_{5/2}$ and $^{4}\Delta_{7/2^{-}}^{4}\Delta_{7/2}$. This transition is analogous to the $1 \mu$m transition of FeH and FeF. A rotational analysis of a number of bands in each subband has been obtained and spectroscopic constants extracted. The lower $a^{4}\Delta$ state is affected by perturbations from a nearby electronic state while the excited $g^{4}\Delta$ state is free from perturbation. This work represents the first observation of a transition involving the quartet states of FeCl