Spectroscopic investigation of a low current arc in pure fluorine

Abstract

A pure fluorine 10-A DC arc has been operated in an Al/sub 2/O/sub 3/ tube of 18 mm diameter at atmospheric pressure. This arc was used to perform radially resolved spectroscopic end-on measurements in the visible and UV-spectral regions. An excitation temperature of 7800 K on the arc axis was determined from the intensity of atomic fluorine lines, and an ion density of 1.7*10/sup 21/ m/sup -3/ was determined from the half-width of the contamination line H/sub beta /. A Boltzmann plot of the affinity continuum in the UV-spectral region yields two groups of electrons. A group of hot electrons is characterized by a temperature that agrees with the excitation temperature, and a group of cold electrons has a temperature in accordance to the gas temperature of 4000 K. The absolute intensity of the affinity continuum gives and electron density of 1.3*10/sup 20/ m/sup -3/ on the arc axis, which is lower than the density of both positive and negative ions in the discharge. From the difference between the electron and gas temperature, an elastic collision cross section between the electrons and F-atoms of 2*10/sup -20/ m/sup 2/ is determined. >