15min:

MAN-CHOR CHAN, SHUN-HING YEUNG, YUNGFENG LI, YUEN-YEE WONG, KAN-HING YIM AND WANG-MING CHAN, Department of Chemistry, The Chinese University of Hong Kong, Shatin, N. T., Hong Kong.

Near infrared absorptions (~11000-13000 cm^-1) of a gaseous plasma generated by discharging a gas mixture of He and CH₄ (at a ratio of 220:1 to give a total pressure of ~860 mTorr) was studied using a high-resolution Ti:sapphire laser spectrometer. Using a home-built AC high voltage power supply and a 2 m long multi-traversal hollow cathode discharge cell equilibrated at ~210 K, a peak-to-peak discharge current of 1-1.5 A was maintained for the plasma. The absorption signals were detected using phase-sensitive detection with concentration modulation at ~5-10 kHz. In addition to the absorptions due to the Phillips band system (¹Pi_u ~ -- ~ ¹Sigma_g electronic transitions) of C₂, several unidentified bands were also observed with good signal-to-noise ratio. Based on the earlier work of Ballik and Ramsey, and S. P. Davis et al., the analysis of the spectrum is underway.