15min:

ANTHONY J. MERER AND JAMES R. D. PEERS, Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, BC, Canada V6T 1Z1; SCOTT J. RIXON, Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, BC, Canada V6T 1Z1.

ZrC 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 and 12 orbitals (both formed from Zr 5s ~ + C 2p ); the evidence is that the small spin-spin interaction of the X^{3 +} ground state ( ₀ = 0.5142~cm^-1, r₀ = 1.807~Å for ⁹⁰Zr¹²C) is consistent with a ' configuration, while the anomalous ¹²C/¹³C isotope shifts and vibrational intervals of the remaining three states show that they all have the same (^{1 +}) symmetry. In particular, the tightly bound a^{1 +} state (T₀ = 187.83~cm^-1, r₀ = 1.739~Å) arises from the 11 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 states (two singlets and two triplets) are observed and can be explained by the promotion of either electron to a orbital; these exhibit both isoconfigurational (¹ /³ ₁) and interconfigurational (¹ /¹ or ³ /³ ) interactions. Details of the rotational and ⁹¹Zr (I=5/2) hyperfine structures will be presented.