ELECTRONIC SPECTROSCOPY OF IRON MONOCARBIDE

$^{a}$ W. J. Balfour, J. Cao, C. V. V. Prasad, and C. X. W. Qian, J Chem. Phys. 74, 3584 (1995).Author Institution: University of UtahThe first $3d$ metal monocarbide to be identified in the gas phase by its electronic spectrum was $FeC^{a}$. In that study, many vibronic bands were identified between 430 and 500 nm. We have extended the range of the original investigation down to 962 nm by probing FeC molecules via resonant two-photon ionization spectroscopy. Iron carbide was produced in our study by reacting laser vaporized iron atoms with methane sealed in a helium supersonic expansion. Between $12.000\;cm^{-1}$ and $18.100\;cm^{-1}$ we have found numerous new transitions. We have rotationally resolved twenty one of the observed bands and have found that all originate from an $\Omega^{\prime} = 3$ state, confirming the ground state assignment of Balfour. The transitions can be assigned as arising from excitation to at least six different electronic states, three with $\Omega^{\prime} = 3$, one with $\Omega^{\prime} = 4$ and at least two with $\Omega^{\prime} = 2$. One of the $\Omega^{\prime} = 3$ states displays a long progression with $\omega_{e}{^{\prime}} = 734.2 \pm 2.0\;cm^{-1}$. The other $\Omega^{\prime} = 3$ states are nearly vertical transitions with only the origin band of each observed. The $\Omega^{\prime} =4$ state displays a progression with $\omega-e^{\prime} = 910.8\;cm^{-1}$. The bands arising from excitation to $\Omega^{\prime} = 2$ cannot be so easily grouped into electronic states. No definite progression have been identified due to very irregular band spacings, but at least two electronic states with $\Omega = 2$ are involved. The weighted average bond length for $^{56}Fe^{12}C$ in the $^{3}\Delta_{3}$ ground state was determined to be $r_{0}= 1.59643 \pm 0.00006$ {\AA}, in good agreement with previous work. By using two different wavelength photons for photoionization it was possible to determine the IP of FeC to be $7.74\pm 0.09$ eV