10min:

S. M. SICKAFOOSE, M. D. MORSE, Department of Chemistry, University of Utah, Salt Lake City, UT 84112; AND D. A. HALES, Department of Chemistry, Hendrix College, Conway, AR 72032.

Resonant two-photon ionization spectroscopy has been used to provide the first rotationally resolved work involving multiply-bonded mixed early-late (or Brewer-Engel) transition metal dimers. The mixed metal dimers TiCo and ZrCo are shown to possess ^{2 +} ground states, in agreement with previous matrix isolation ESR studies. Two previously observed vibronic bands in ZrCo were rotationally resolved, as was one of several newly discovered vibronic transitions in TiCo. Ground state rotational constants for ⁴⁸Ti⁵⁹Co and ⁹⁰Zr⁵⁹Co were measured to be B₀ '' = 0.18615(8) cm^-1 and B₀ '' = 0.11909(7) cm^-1, giving r₀ '' = 1.8508(4) Å and r₀ '' = 1.9941(6) Å, respectively. In both molecules the ground state conforms to the Hund's case b _S coupling scheme, with Fermi contact interactions between the unpaired electron and the ⁵⁹Co (I = 7/2) nucleus of b_F '' = 0.0468(7) cm^-1 for ⁴⁸Ti ⁵⁹Co and b_F '' = 0.0551(7) cm^-1 for ⁹⁰Zr ⁵⁹Co. These values indicate that the unpaired electron occupies a orbital having 32% and 37.5% Co 4s character in TiCo and ZrCo, respectively. All three of the rotationally resolved bands are ² _3/2 X^{2 +} transitions. For ⁹⁰Zr⁵⁹Co the 0 - 0 and 1 - 0 bands were resolved at ₀ = 10496.1690(44) cm^-1 and 10884.4266(24) cm^-1, giving B₀ ' = 0.11922(8) cm^-1 and B₁' = 0.11962(6) cm^-1. For ⁴⁸Ti⁵⁹Co the rotationally resolved band had ₀ = 9873.8342(19) cm^-1 and B' = 0.19107(6) cm^-1. These results will be discussed in the context of prior work on these and related molecules.