TIME-RESOLVED DIODE LASER SPECTROSCOPY OF THE $v_{3}$ BAND OF THE IRON DICARBONYL RADICAL $Fe(CO)_{2}$

[1] K. Sakaguchi, K. Tanaka, and T. Tanaka, to be published. [2] Y. Kasai, Y. Ohshima, and Y. Endo, to be published.Author Institution: Department of Chemistry Faculty of Science, Kyushu UniversityThe $v_{3}$ (CO antisym. stretch) fundamental band of $Fe(CO)_{2}$ was observed by time-resolved infrared diode laser spectroscopy. The $Fe(CO)_{2}$ radical was produced by 193 nm ArF exeimer laser photolysis of iron pentacarbonyl $Fe(CO)_{5}$. More than 50 lines in the $1924-1932 cm^{-1}$ region have been assigned to the $v_{3}$ fundamental band of $Fe(CO)_{2}$. Observed spectra are split into triplet, $\Omega = 0, 1^{e}$, and $1^{f}$, due to spin-spin interaction. The spectral lines which have even $N$ quantum number are missing due to the spin statistics of C (I=0) and O (I=0) nuclei. The observation indicates definitely that $Fe(CO)_{2}$ is a linear molecule with $D_{xh}$ symmetry and the ground electronic state is $^{3}\Sigma_{g}$. The rotational and centrifugal distortion constants determined are 1419.80(49) MHz and 4.73(37) kHz, respectively. The spin-spin interaction constant $\lambda_{0}$ determined is as large as 676 (56) GHz, which is comparable with that of FeCO (659 GHz) [1], but is much larger than that of $Fe(CO)_{3}$ (12 GHz) [2]. The $v_{3}$ band origin 1928. 19023(52) $cm^{-1}$ is lower than that of the $v_{1}$ band of FeCO, $1946.4706 cm^{-1}$ [1]