NUCLEAR HYPERFINE STRUCTURE IN THE $X^{3}\Sigma^{+}$ STATE OF $^{91}$ZrC

Author Institution: Department of Physics and Astronomy, University of British Columbia; Department of Chemistry, University of British ColumbiaElectronic bands of zirconium monocarbide, ZrC, can be observed following the reaction of laser-ablated Zr atoms with methane under supersonic free-jet conditions. In our experiments some of the bands near $17000 cm^{-1}$ are strong enough for nuclear hyperfine structure from the $^{91}$Zr isotope ($I = 5/2, 11.22%$ abundance) to be assignable. Hyperfine splittings of up to $0.2 cm^{-1}$ are found in some of the rotational lines. Analysis shows that the principal hyperfine effects are in the $^{3}\Sigma$ ground state, where $b = -0.03132 \pm 0.00015 cm^{-1}$ and $c = -0.00122 \pm 0.00038 cm^{-1} (3\sigma$ error limits). The large Fermi contact parameter, b, indicates that an unpaired $Zr 5 s \sigma$ electron is present, which, taken together with the small value of $\lambda (0.5139 cm^{-1})$, means that the ground state must be a $^{3}\Sigma^{+}$ state, from the electron configuration $(Zr 5 s \sigma)^{1} (C 2p\sigma)^{1}$. Internal hyperfine perturbations occur between the $F_{1}$ and $F_{3}$ electron spin components of the ground state in the range $N = 2 - 4$, producing extra lines in some of the branches; the perturbations are of the type $\Delta N = 0, \Delta J = \pm 2$, and are a second order effect arising because the $F_{1}$ and $F_{3}$ spin components ($J = N + 1$ and $J = N - 1$, respectively) both interact with the $F_{2}$ component $(J = N)$ through $\Delta N = 0, \Delta J = \pm 1$ matrix elements of the Fermi contact operator