ANALYSIS OF SINGLET AND TRIPLET STRUCTURE IN THE HIGH-RESOLUTION SPECTRUM OF ZIRCONIUM MONOCARBIDE

$^{a}$ Present address: Creo Inc., 3755 Willingdon Avenue, Burnaby, BC, Canada V5G 3H3Author Institution: Department of Chemistry, University of British Columbia; Department of Physics and Astronomy, University of British ColumbiaZrC is readily produced in supersonic expansion via reaction of 1% methane (in helium) with laser-ablated zirconium metal. Laser-induced fluorescence excitation and dispersed emission spectra have been recorded for bands in the region $630 - 520$ nm $(16000 - 19000 cm^{-1})$. The four lowest electronic states lie below $2500 cm^{-1}$ and appear to represent all possible arrangements of two electrons in the two nearly degenerate $11\sigma$ and $12\sigma$ orbitals (both formed from $Zr 5s\sigma + C 2p\sigma)$; the evidence is that the small spin-spin interaction of the $X^{3}\Sigma^{+}$ ground state $(\lambda_{0} = 0.5142 cm^{-1}, r_{0} = 1.807$ {\AA} for $^{90}Zr^{12}C)$ is consistent with a $\sigma \sigma^{\prime}$ configuration, while the anomalous $^{12}C/^{13}C$ isotope shifts and vibrational intervals of the remaining three states show that they all have the same $(^{1}\Sigma^{+})$ symmetry. In particular, the tightly bound $a^{1}\Sigma^{+}$ state ($T_{0} = 187.83 cm^{-1}, r_{0} = 1.739$ {\AA}) arises from the $11\sigma^{2}$ closed shell configuration. Moreover, this molecular orbital scheme is consistent with the confused level structure above $16000 cm^{-1}$. At least four close-lying II states (two singlets and two triplets) are observed and can be explained by the promotion of either $\sigma$ electron to a $\pi$ orbital; these exhibit both isoconfigurational $(^{1}\Pi/^{3}\Pi_{1})$ and interconfigurational $(^{1}\Pi/^{1}\Pi$ or $^{3}\Pi/^{3}\Pi)$ interactions. Details of the rotational and $^{91}Zr (I = 5/2)$ hyperfine structures will be presented