Pure rotational spectra of the rare isotopologues of titanium oxide, (TiO)-Ti-46, (TiO)-Ti-47, (TiO)-Ti-49, and (TiO)-Ti-50, have been recorded using a combination of Fourier transform millimeter-wave (FTmmW) and millimeter/submillimeter direct absorption techniques in the frequency range 62-538 GHz. 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 N2O 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 (TiO)-Ti-47 and (TiO)-Ti-49, 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, (TiO)-Ti-48, 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.

New laboratory measurements of hydrides have been carried out using terahertz direct absorption spectroscopy. Spin components of the N = 2 <- 1 transition of the free radical CrH (X (6)Sigma(+)) have been recorded in the range 730-734 GHz, as well as a new measurement of the J = 2 <- 1 line of AlH (X (1)Sigma(+)) near 755 GHz. Both species were created in an AC discharge of H-2, argon, and metal vapor. For CrH, the chromium source was Cr(CO)(6), while AlH was produced from Al(CH3)3. The J = 4.5 <- 3.5 and 3.5 <- 2.5 fine-structure components were recorded for CrH, each which consists of resolved proton hyperfine doublets. For AlH, the two main quadrupole components, F = 4.5 <- 3.5 and 3.5 <- 2.5, of the J = 2 <- 1 transition were observed as blended features. These data were analyzed with previous 1 <- 0 millimeter/submillimeter measurements with (6)Sigma and (1)Sigma Hamiltonians for chromium and aluminum hydrides, respectively, and rotational, fine-structure (CrH only), and hyperfine constants were derived. The new measurements have resulted in refined spectroscopic parameters for both species, as well as direct measurement of the respective 2 <- 1 rotational transitions. This work also resolves a 10 MHz discrepancy in the frequency of the AlH line. CrH and AlH have already been observed in the photospheres of stars via their electronic transitions. These data will facilitate their discovery at submillimeter/terahertz wavelengths in circumstellar envelopes and perhaps in diffuse clouds.