Far-infrared LMR spectroscopy of NF a1Δ (v = 0, 1, 2)

Far-infrared LMR spectra of NF in its a¹Δ state have been detected and assigned. Lines in two rotational transitions of both v = 0 and v = 1 states were measured for analysis. The derived constants are in excellent agreement with earlier EPR work (hyperfine parameters, v = 0) and with diode laser spectroscopy (rotational constants for v = 0 and 1). Using the optimized parameters it is shown that there is a significant decrease in the fluorine hyperfine constant on vibrational excitation. One rotational transition from $\text{v = 2}\text{NF}{}^1\text{Δ}$ has also been assigned.