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 TiCl⁺ (X³ _r) has been measured using millimeter-wave direct absorption methods incorporating velocity modulation techniques. This species is the first metal-containing molecular ion observed with millimeter-wave velocity modulation spectroscopy. TiCl⁺ was created in an AC glow discharge of gas-phase TiCl₄ and argon. Ten, eleven, and nine rotational transitions of ⁴⁸Ti³⁵Cl⁺, ⁴⁸Ti³⁷Cl⁺, and ⁴⁶Ti³⁵Cl⁺ were measured, respectively, in the frequency range of 323 to 424 GHz. All three spin-orbit components were observed. The irregular fine structure splittings indicate that two spin-orbit ladders are perturbed by an excited ³ _r electronic state. Rotational, spin-orbit, and spin-spin parameters have been determined from the data and agree well with past optical studies. This study illustrates the power of velocity modulation for ion selectivity at millimeter/sub-mm wavelengths.