AN INFRA-RED ELECTRONIC TRANSITION OF CoC

The laser induced fluorescence spectrum of jet-cooled CoC has been measured at high resolution following the reaction of laser-ablated cobalt atoms with methane. The ${^{2}}\\Sigma^{+}$ ground state is an unusually good example of Hund's case $(b_{\\beta S})$ coupling. Since $^{59}Co$ has a nuclear spin l = 7/2, each rotational level is split by the Fermi contact interaction into G = 3 and 4 components, where G = I + S; the splitting is roughly 4b, and for N = 0 is more than $0.5 cm^{-1}$. The ${^{2}}\\Sigma^{+}$ state begins to uncouple toward case $(b_{\\beta J})$ at higher N values. We have identified three upper state $\\Pi$ levels giving rise to bands at $13078 cm^{-1} (\\Omega = 3/2), 13344 cm^{-1} (\\Omega = 1/2)$ and $13428 cm^{-1} (\\Omega = 3/2)$; only transitions to the first two are strong enough to be recorded at high resolution. There are three more $\\Pi$ levels approximately $1000 cm^{-1}$ higher in energy. Furthermore, we have identified a very low-lying ${^{2}}\\Delta_{i}$ state, for which the $\\Omega = 5/2$ and 3/2 levels lie at 222 and $1173 cm^{-1}$, respectively. Laser excitation of the ${^{2}}\\Pi_{3/2} - {^{2}}\\Delta_{5/2}$ transition has been observed by monitoring the strong ${^{2}}\\Pi_{3/2} - {^{2}}\\Sigma^{+}$ emission, which has allowed the ${^{2}}\\Delta_{5/2}$ state to be characterized at high resolution. A total of 879 hyperfine transitions between the various ${^{2}}\\Pi_{1/2}, {^{2}}\\Pi_{3/2} {^{2}}\\Delta_{5/2}$ and ${^{2}}\\Sigma^{+}$ states has been assigned and fitted. The $\\Pi$ and $\\Delta$ states were treated with a case (c) model and the ${^{2}}\\Sigma^{+}$ state in case $(b_{\\beta S})$, following the full derivation of the appropriate matrix elements.