Determination of a hydrocarbon concentration in the N₂dc flowing afterglow and its application

On the basis of spectroscopical measurements, a method for the determination of hydrocarbon concentration has been proposed and realized in practice. This simplified method is based on an integral measurement of intensity of the optical emission spectrum by a semiconductor photodetector in the nitrogen afterglow at low temperatures. The advantage of the proposed method is its technical simplicity and the economy of the measuring equipment. We used a photodiode BPW34B with increased sensitivity in the spectral range 300-400 nm as a detector. The detection limit of our method is in the order of 10 9 carbon atoms in pure nitrogen. A kinetic model of the energy transfer processes during the afterglow of pure nitrogen with hydrocarbon traces is given. It can successfully explain the observed results and also provides a good explanation of the quenching of nitrogen `pink afterglow' by hydrocarbon traces. The value of the rate coefficient of the main afterglow reaction N 2 ( X , 1 Σ g + , v ⩾12) + CN ( X 2 Σ)→ N 2 ( X 1 Σ g + ) + CN ( B 2 Σ + ) was predetermined about 1.2 × 10 -11 cm 3 s -1 at room temperature. The method was used for the determination of polymeric material degradation at low pressures.