2004ApJ...611L..65H

The N=0⟶1 rotational transition of CrH and the N=1⟶2 transition of CrD have been recorded in their X⁶Σ⁺ ground electronic states using submillimeter direct absorption spectroscopy. Both species were created in a DC discharge by the reaction of chromium metal, vaporized in a Broida-type oven, with H₂or D₂. Because of the presence of five unpaired electrons, as well as the proton or deuterium nuclear spin, these transitions exhibit complicated fine structure and hyperfine splittings. The five strongest hyperfine transitions were measured for CrH and are split over a 60 GHz region because of spin-spin and spin-rotation interactions. Seven lines have also been recorded for CrD arising from four spin components. The data have been analyzed with a Hund's case b Hamiltonian, resulting in improved constants for both species. These data are crucial for submillimeter searches for CrH toward interstellar and circumstellar gas. Electronic transitions of CrH have been routinely observed in L dwarf and brown dwarf atmospheres, suggesting its presence in other astronomical regions.