15min:

D. T. HALFEN AND L. M. ZIURYS, Department of Chemistry, Department of Astronomy, and Steward Observatory, University of Arizona, Tucson, AZ, 85721.

The pure rotational spectrum of the molecular ion FeCO⁺ (X^{4 -}) has been measured using millimeter-wave direct absorption methods incorporating velocity modulation techniques. This work is the first gas-phase study of FeCO⁺ by any spectroscopic method. FeCO⁺ was created in an AC glow discharge of gas-phase Fe(CO)₅ and argon. Eleven rotational transitions were measured in the frequency range of 323 to 408 GHz. The four fine structure components exhibited very large spin splittings, indicating a high degree of Hund's case (a) character and large second-order spin-orbit interactions. The data has been fit with a case (b) Hamiltonian and rotational and fine structure constants were obtained. FeCO⁺ may be prevalent in interstellar/circumstellar gas given the large abundance of CO.