The Deltav = 0 sequence of the NF(b(1)Sigma (+)v'-->X(3)Sigma -v ") spin forbidden emission is studied from the intensity point of view. The NF b(1)Sigma (+) emitting state is produced by NF3 windowless photolysis in a microwave flowing afterglow apparatus. Although the observed NF b(1)Sigma (+) vibrational population is at a Boltzmann equilibrium, v' = I through v' = 3 emitting levels appear to be depleted. This behaviour is attributed to interactions of the emitting b(1)Sigma (+) state with the ground state continuum. A value of 60.7+/-1.5 kcal/mol for the NF X(3)Sigma (-) dissociation limit is thus estimated.