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Description
Pure rotational spectra of the rare isotopologues of titanium oxide, ^46^TiO, ^47^TiO, ^49^TiO, and ^50^TiO, have been recorded using a combination of Fourier transform millimeter-wave (FTmmW) and millimeter/submillimeter direct absorption techniques in the frequency range 62-538GHz. This study is the first complete spectroscopic characterization of these species in their X^3^{Delta}_r_ ground electronic states. The isotopologues were created by the reaction of N_2_O or O_2_ and titanium vapor, produced either by laser ablation or in a Broida-type oven, and observed in the natural Ti isotopic abundances. Between 10 and 11 rotational transitions J+1<->J were measured for each species, typically in all 3 spin-orbit ladders {Omega}=1, 2, and 3. For ^47^TiO and ^49^TiO, hyperfine structure was resolved, originating from the titanium-47 and titanium-49 nuclear spins of I=5/2 and 7/2, respectively. For the {Omega}=1 and 3 components, the hyperfine structure was found to follow a classic Lande pattern, while that for {Omega}=2 appeared to be perturbed, likely a result of mixing with the nearby isoconfigurational a^1^{Delta} state. The spectra were analyzed with a case (a) Hamiltonian, and rotational, spin-orbit, and spin-spin parameters were determined for each species, as well as magnetic hyperfine and electric quadrupole constants for the two molecules with nuclear spins. The most abundant species, ^48^TiO, has been detected in circumstellar envelopes. These measurements will enable other titanium isotopologues to be studied at millimeter wavelengths, providing Ti isotope ratios that can test models of nucleosynthesis.
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