Introduct.ionThe process of the formation of electrical discharge in gases is greatly dependent on the electrode surface quality.The probability of releasing secondary electrons from clean iiietal surfaces, or from metal surfaces covered with oxide layers depends on the work function of the cathode material. Iinpiirities and oxide layers on the cathode surface decreaRe8 the work func-Secondary einission of electrons due to the bombardment of the cathode surface with ions and excited a t o m or molecules has an important role in the discharge in gasfilled diodes, a t pressures lower than the atmospheric. For most gases secondary emission of electrons from the cathode due to the bombardment with positive ions is predominant. However, the influence of secondary emission induced by nietastable atoms or niolecules of some gases can not be ignored. For example, for the argon-filled diodes with tantaliliii electrodes, coefficients of secondary emission of electrons due to the bombardment with positive ions and nietastable atoms are very close being 0.023 and 0.022, respectively. Siniilarly for the argon-filled diodes with molybdenum electrodes the corresponding values are 0.065 a n d 0.071 [l].Detailed experimental as well as theoretical investigations of the gas discharge in nitrogen-filled diodes [2--81 show that a t E/p = 75 V cni-1. inbar-' the secondary emission of electrons due to the bombardment of the cathode surface with N2(A3L',,+) metable moleciiles, diffusing through the gas, has n predominat role. The nuniber of secondav emission electrons induced by metastable nitrogen molecules per unit cathode surface depend on the coefficient of secondary emission as well as on the nriinber of X2 metastables which per second arrive a t the correqponding cathode siirface [5]. There are a few nietliods for the detection of inetastable atonis or iiiolecules in gases, the optical ones are generally adopted, but they are efficient only a t high concentrations (> 10'3 c1iir3) of inetastable atoms or molecules in gases [g].
