Intensity ratio of spectral bands of nitrogen as a measure of electric field strength in plasmas

The ratios of intensities of the spectral bands of molecular nitrogen corresponding to transitions N + (B 2 � + g ,v = 0) → N + (X 2 � + ,v = 0), N2(C 3 � u ,v = 0) → N2(B 3 � g ,v = 0) and N2(C 3 � u ,v = 2) → N2(B 3 � g ,v = 5) as a function of the applied electric field strength were measured for air in the pressure range of 300 to 10 5 Pa. The non-self-sustaining dc discharge in a parallel-plane gap was used for excitation of gas molecules. The reduced field strength was varied in the range of (150–5000) × 10 −21 Vm 2 . The measured ratio of intensities as a function of electric field strength is compared with the theoretical estimates made by other authors. The obtained intensity ratio versus field strength curves can be used for field strength estimation in plasmas if the nitrogen molecules are excited dominantly from the ground state directly by the electron impact. (Some figures in this article are in colour only in the electronic version)