The Far-Infrared Rotational Spectrum of X^2∏ OH Notes

We have previously reported the direct (zero-field) measurement of the fundamental rotational transitions of the hydroxyl radical using a recently developed far-infrared (FIR) laser sideband spectrometer (/). This note presents a more extensive set of measurements of the pure rotational spectrum of OH, which we combine with existing microwave, infrared, and optical data to produce an optimized set of molecular constants.