MILLIMETER-WAVE SPECTROSCOPY OF THE FeCO($X^3\Sigma^-$) AND FeNO($X^2\Delta_i$) RADICALS IN THE VIBRATIONAL EXCITED STATES

Author Institution: Department of Chemistry, Faculty of Science, Kyushu University,; Hakozaki, Higashiku, Fukuoka, 812-8581 JAPANRotational spectra of the FeCO and FeNO radicals produced by UV laser photolysis in the vibrational excited states were measured in the millimeter-wave region with the conventional absorption cell at room temperature. The rotational transitions of the FeCO radical in the ground and $\nu_2$ states have been observed by millimeter-wave spectroscopy}, 106, 6820-6824 (1997)}, and the $\nu_1$ fundamental band and hot band from $\nu_2$ state also have been studied by infrared diode laser spectroscopy. In the present work, the rotational transitions ($J$ = 33 - 32 $\sim$ 37 - 36 ) in the $\nu_3$ state of the $X^3\Sigma^-$ state were observed to split into 3 components due to the spin-rotation and spin-spin interactions. Molecular constants including rotational constant and centrifugal distortion constant were determined by a least squares fitting. The equilibrium rotational constant $B_e$ was calculated to be 4373.405(72) MHz from the vibration rotation constant $\alpha_{\rm 3}$ = 20.2051(42) MHz, and previously reported $\alpha_{\rm 1}$ and $\alpha_{\rm 2}$. The bond length between Fe and C, calculated to be 1.725 ${\rm \AA} $ assuming $r_{\rm CO}$= 1.159 ${\rm \AA}$, agrees well with the {\it ab initio} result, $r_{\rm FeC} = 1.722$ \AA}. The 2$\nu_2$ state split into 9 substates due to the vibronic interaction, and the rotational transitions in the $P = 0$ component were observed. The rotational transitions of the FeNO radical in the ground and $\nu_2$ states}, and the $\nu_1$ band have been observed in the millimeter-wave and infrared region, respectively. The rotational transitions ($J$ = 28.5 - 27.5 $\sim$ 32.5 - 31.5 ) in the 2$\nu_2$ state of the $X^2\Delta_i$ state were observed in the present study. The 2$\nu_2$ state ($\Omega = 5/2$) splits into 3 substates, $^2\Gamma_{P = 9/2}, ^2\Delta_{P = 5/2}$ and $^2\Sigma_{P = 1/2}$, due to the vibronic interaction. The absorption lines in the $^2\Sigma_{P = 1/2}$ state split into two components because of the $p$-type doubling. The transition in the $\nu_3$ state is now under survey to determine the constant $\alpha_3$ and the equilibrium rotational constant