Addition of sulphur hexafluoride to the nitrogen afterglow was found to selectively quench the δ and γ bands of NO while enhancing markedly the β bands involving v' = 1 and 2 levels. These effects could be satisfactorily explained on the basis of vibrational relaxation in the a4π state brought about by collisions with SF6and the interactions of this state with the other excited states which are involved in the emission of the above band systems. Certain peculiar spectral features were also observed at the crossing of the b4σ−with the B2π state.