A STUDY OF MOLECULAR ION DISTRIBUTION IN THE POSITIVE COLUMN OF D.C. GLOW DISCHARGES BY DIODE LASER SPECTROSCOPY

$^{1}$N.N. Haese, F.S. Pan, and T. Oka, Phys. Rev. Lett., 50, 1575 (1983).Author Institution: Department of Chemistry and Department of Astronomy, and Astrophysics, The University of ChicagoThe high spatial resolution of laser infrared ion spectroscopy enables us to monitor the distribution of molecular ions in situ in the discharges. We observed the radial distribution of ion densities in the positive column of glow discharges using strong absorption lines of $ArH^{+}$ and $H_{3}{^{+}}$. The results show a remarkable depletion of ion densities in the center of plasma for the high current density (400mA/cm) and/or high pressure (10 torr) regime. The very high abundance of $ArH^{+}$ allows us to measure also the translational, rotational and vibrational temperatures. Together with our previous study of ion $mobility,^{1}$ this method provides us with a powerful means of plasma diagnostics which is sensitive to quantum state