Application of microwave breakdown spectroscopy to detect halide impurities in the air

In order to determine ppm orders of air pollutants, e.g., halide impurities , spectroscopy of the photons emitted from the plasma generated by a focuse d microwave beam in the air has been applied. The microwave beam was suppli ed by a pulsed magnetron (microwave frequency: 9.4 GHz; peak intensity: 100 kW; pulse width: 5 mus; pulse repetition frequency: 10 Hz), focused in a v acuum chamber, where pressure and impurities had been controlled to target values, and a plasma was generated using the air there. At the same time, t he energy spectrum of the photons from the plasma was measured to determine the concentrations of chlorine and fluorine in the air by a measurement sy stem consisting of a diffraction grating, streak camera, and charge-coupled -device camera. As a result of preliminary experiments, where the concentra tion of CCl2F2 was changed from 0.05 to 2 vol % in decompressed air (pressu re: 10 Torr), it was demonstrated that 1700 ppm of chlorine could be determ ined from the background spectrum caused by the first positive band of nitr ogen (B(3)Pi (g)-A(3)Sigma (+)(u)), its second positive band (C(3)Pi (u)-B( 3)Pi (g)), and first negative band (B(3)Sigma (+)(u)-X(2)Sigma (+)(g)). The experimental data demonstrated that ppm orders of halide impurities can be determined by improving pulse repetition frequency of the microwave source . (C) 2001 American Institute of Physics.