The identification of a ⁶Φ-X ⁴δ intercombination system in the FeH radical at 448 nm

A new band system has been discovered in the electronic spectrum of the FeH radical at 448 nm. The spectrum has been recorded at Doppler resolution by laser excitation spectroscopy with a sample at ambient temperatures, produced by the gas phase reaction between H atoms and iron pentacarbonyl Fe(CO) ₅. The fluorescence excited when the laser is tuned to individual rotational lines has also been dispersed. These experiments show that the light is emitted almost wholly at longer wavelengths into the 492 nm system (the "blue" system). The 448 nm system has been assigned as a ⁶Φ-⁴Δ transition; the lower state is shown to be the X ⁴Δ state previously characterized by Phillips et al. Accurate term values are obtained for two spin components in the ⁶Φ state, designated the g ⁶Φ state. The dispersed fluorescence experiments show that the lower state of the 492 nm system is the a ⁶Δ state and that it lies about 2060 cm^-1 above the X ⁴Δ state. A conclusion of this study is that the 492 nm system of FeH involves the g 6Φ-α ⁶Δ transition.