KEIICHI TANAKA, T. HIKITA AND T. TANAKA, Department of Chemistry, Kyushu University, Fukuoka, 812-8581 Japan.
Time-resolved infrared diode laser spectroscopy was applied to the observation of the 1 + 2 - 2 hot band of the iron carbonyl (FeCO) radical. The FeCO radical was produced by the ArF excimer laser photolysis of iron pentacarbonyl Fe(CO)5. Although the FeCO radical has the 3 - electronic ground state, the 2 bending vibrational excited state has vibronically the 3 symmetry, which allows the vibronic interaction with the 3 electronic state located very closely, 6400 cm-1, to the ground electronic state .
In the frequency region of 1930-1950 cm-1, more than 50 R- and P-branch lines were identified which split into triplet (P = 0, 1, and 2) due to the spin-spin interaction. Each spin component split further into doublet, as -type doubling, because of the vibraonic interaction with the nearby 3 electronic state. The band origin 0 = 1941.54573 (50) cm-1 was determined as well as the molecular constants for the 1 + 2 state, fixing the molecular constants for the 2 state to those of the millimeter-wave . results. The effective spin-orbit constant Aeff and the -type doubling constants for the 1 + 2 state are much different from those of the 2 state indicating that the effect of vibronic interaction with the 3 electronic state has increased due to the excitation of the 1 vibration.