Continuum Radiation in an Argon Positive Column

Abstract

A weak continuum with a maximum near 3100 Å is radiated from the positive column of an argon normal-glow discharge. The intensity distribution of this continuum (observed here from 2900 to 7000 Å) does not correspond to that of a free—free, free—bound recombination spectrum. The continuum intensity, the 3P2 metastable population, and the relative populations of more energetic atomic states are examined as functions of pressure (5–30 torr) at constant currents and as functions of current (0.5–5 mA) at constant pressures. It is shown that the continuum is best represented as radiation emitted in transitions from weakly bound molecular states to dissociative molecular states, where the radiating molecular states are populated by electron excitation from metastable molecules formed by three-body conversion of metastable atoms.