Resonance enhanced multiphoton ionization as a diagnostic tool in glow discharge plasmas

Resonance enhanced multiphoton ionization (REMPI) has been used to quantita tively detect benzene in an Ar dc plasma. The plasma reactor was fabricated from a 5 cm diam Pyrex tube that was about 30 cm long. The reactor also po ssessed two plasma electrodes that were separated by 3 cm. The plasma was g enerated at 160 mTorr pressure under continuous flow of Ar that was seeded with 100-1000 ppm of benzene. Ions generated by REMPI were detected using a separate electrode placed at the edge of the plasma zone. We were able to obtain well-resolved and unambiguous benzene REMPI spectra in the 250-265 n m laser wavelength under a broad range of plasma conditions. The spectra ob tained were well resolved, exhibited sharp spectral features and were in co mplete agreement with the results reported in the literature under nonplasm a conditions. Measured REMPI signal intensities also were linearly proporti onal to the benzene concentration, suggesting that REMPI can be a useful qu antitative plasma diagnostic. (C) 2000 American Vacuum Society. [S0734-211X (00)12103-1].