The submillimeter spectrum of MnH and MnD (X⁷Σ ⁺)

The submillimeter-wave spectrum of the MnH and MnD radicals in their ⁷Σ⁺ ground states has been measured in the laboratory using direct absorption techniques. These species were created in the gas phase by the reaction of manganese vapor, produced in a Broida-type oven, with either H₂ or D₂ gas in the presence of a DC discharge. The N = 0 → 1 transition of MnH near 339 GHz was recorded, which consisted of multiple hyperfine components arising from both the manganese and hydrogen nuclear spins. The N = 2 → 3 transition of MnD near 517 GHz was measured as well, but in this case only the manganese hyperfine interactions were resolved. Both data sets were analyzed with a Hund's case b Hamiltonian, and rotational, fine structure, magnetic hyperfine, and electric quadrupole constants have been determined for the two manganese species. An examination of the magnetic hyperfine constants shows that MnH is primarily an ionic species, but has more covalent character than MnF. MnH is a good candidate species for astronomical searches with Herschel, particularly toward material associated with luminous blue variable stars.