Submillimeter spectroscopy on OH(+) - The rotational transition at 1 THz

A report is presented of the first observation and complete analysis of the spin multiplet and hyperfine structure of the lowest rotational transition (N = 0 to 1) in the X 3 Sigma -, v = 0 ground state of the hydroxyl cation OH(+). The discussed study provides molecular constants for the ground state and yields accurate frequencies for the lowest transitions which may facilitate detection of OH(+) in interstellar clouds. The observed spectrum has been fitted to an appropriate Hamiltonian describing the rotational and fine structure and the magnetic hyperfine structure of a 3 Sigma state. 12 references