15min:

DALE J. BRUGH, National Institute of Standards and Technology, Optical Technology Division, Gaithersburg, MD 20899; TJ RONNINGEN AND MICHAEL D. MORSE, University of Utah, Department of Chemistry, Salt Lake City, UT 84112.

In a continuing effort to understand the nature of the metal carbon bond in transition metal monocarbides we have undertaken the first spectroscopic investigation of MoC by resonant two-photon ionization spectroscopy. Molybdenum carbide was produced by laser vaporization of a Mo sample disk in a supersonic expansion of He and 3% CH₄. Using 6.42 eV photons for photoionization we have observed a number of transitions between 17\,700\,cm^-1 and 24\,000\,cm^-1. Twenty four of the observed bands have been studied at sufficient resolution (0.04 cm^-1) to allow the rotational structure of each transition to be resolved. An analysis of the isotope shifts has allowed a tentative identification of three band systems among the 24 observed transitions. A number of the observed bands have remained ungrouped. Every rotationally resolved band appears to be an \Omega = 1 <- 0 transition. Given that the ground state of NbC is known to be 11² 2¹, ²_r and that of RuC is known to be 11² 2⁴, ¹⁺, it seems likely that the addition of another electron on moving from NbC to MoC yields for a ground state the \Omega = 0⁺ component of a ^3- term. This is consistent with the observation that every transition in this study originates from an \Omega = 0 state. The X^3- rotational constant for the most abundant isotope, ⁹⁸Mo¹²C, has been determined to be 0.553640 \pm 0.000055 cm^-1. This corresponds to a ground state bond length of 1.687719 \pm 0.000084 Å.