We perform precision microwave spectroscopy—aided by Stark deceleration—to reveal the low-magnetic-field behavior of OH in its ${}^2\Pi _{3∕2}$ rovibronic ground state, identifying two field-insensitive hyperfine transitions suitable as qubits and determining a differential Landé $g$ factor of $1.267\left(5\right)\times {10}^{-3}$ between opposite-parity components of the $\Lambda$ doublet. The data are successfully modeled with an effective hyperfine Zeeman Hamiltonian, which we use to make a tenfold improvement of the magnetically sensitive, astrophysically important $\Delta F=\pm 1$ satellite-line frequencies, yielding $1720529887\left(10\right)\mathrm{Hz}$ and $1612230825\left(15\right)\mathrm{Hz}$.

• Received 18 August 2006

DOI:https://doi.org/10.1103/PhysRevA.74.061402