Line intensities in the (0,0) band of NF(b (1) Sigma+ --> X (3) Sigma(-)) spin forbidden emission have been observed in a microwave apparatus. Deduced line strengths of the P-O and R-S well resolved branches are shown differently, in contrast with the theoretical prevision, and are interpreted by taking into account some peculiarities of the NF radical. An intermediate (a) and (b) Hund case is seen to apply to P-O and R-S in the whole rotational range examined. Accordingly, a reliable value for the effective transition moment mu(e) is evaluated from the experiment, (C) 1997 American Institute of Physics.