Knowledge Bank

Time-resolved infrared diode laser spectroscopy was applied to the observation of the $\nu 1+\nu 2-\nu 2$ 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 $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Sigma -$ electronic ground state, the $\nu 2$ bending vibrational excited state has vibronically the $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Pi$ symmetry, which allows the vibronic interaction with the $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Pi$ electronic state located very closely, $6400cm-1$, to the ground electronic $statea$. In the frequency region of $1930-1950cm-1$, 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 A-type doubling, because of the vibraonic interaction with the nearby $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Pi$ electronic state. The band origin $\nu 0=1941.54573(50)cm-1$ was determined as well as the molecular constants for the $\nu 1+\nu 2$ state, fixing the molecular constants for the $\nu 2$ state to those of the millimeter-$waveb$, results. The effective spin-orbit constant $Aeff$ and the A-type doubling constants for the $\nu 1+\nu 2$ state are much different from those of the $\nu 2$ state indicating that the effect of vibronic interaction with the $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Pi$ electronic state has increased due to the excitation of the $\nu 1$ vibration.