Knowledge Bank

Rovibrational transitions of the $\nu 1$ band (N-O stretch) of the FeNO radical were observed in the 1750-1780 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ region. The FeNO radical was produced by 193 nm excimer laser photolysis of Fe(CO)$2$(NO)$2$ and the transient absorption signal was detected by time-resolved infrared diode laser spectroscopy.\ More than 40 lines were assigned to the $\nu 1$ fundamental band of the $\Omega =5/2$ spin component, together with ten $Q$-branch lines ($J$ = 2.5 - 11.5) in the 1760 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ region, to confirm the electronic ground state to be $X2\Delta i$. Effective molecular constants for the $\Omega =5/2$ spin component, including the band origin $\nu 0$ (1767.26093(38) cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$), the rotational constant $B$ (4610.17754(93) MHz) and the centrifugal distortion constant $D$ (1.17003(47) kHz), were derived from a least squares fitting of the observed transitions. The average bond length $rCo-N$ between Co and N was calculated to be 1.621 \AA from the rotational constant $B0$ assuming $r_{\rm N-O} = $1.186 \AA as given by $abinitio$ calculation}, 3915 (2000)}. The $\nu 1$ hot band lines originated from the $\nu 2$ (Fe-N-O bending; 308 cm$^\{-1\}\; ^a$) vibrationally excited state were also observed. Pure rotational lines of FeNO were also observed by the millimeter wave spectroscopy with the UV photolysis of Fe(CO)$2$(NO)$2$}.