Millimeter wave rotational spectra of indium monofluoride

The millimeter wave rotational spectra of indium monofluoride (InF) have been studied in the 250–300 GHz frequency region. Three rotational transitions of¹¹⁵InF in thev=0, 1 and 2 vibrational states and two rotational transitions of the less abundant¹¹³InF in thev=0 state with resolved hyperfine structures have been measured. The analysis including previous measurements on the lower rotational transitions in the microwave region yielded improved and extended sets of Dunham parameters. The comparison of the results for the two isotopic species of InF indicates a similar deviation from the Born-Oppenheimer approximation as for InCl.