Ion- and electron-density decay rates in afterglow plasmas of argon and argon-oxygen mixtures

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Abstract
Measurements are described of the ion and electron decay rates in pure argon and argon-oxygen afterglow plasmas. Mass-spectrometric investigations of the temperature dependence of the rate coefficient for the Ar+/O2 charge-exchange reaction over the vessel wall temperature range 180 to 580 degrees K showed the rate coefficient to decrease from 7.05*10-11 cm3 s-1 to 2.18*10-11 cm3 s-1. A Langmuir probe was used to determine the dissociative recombination coefficients alpha of Ar2+ ions and O2+ ions with electrons in these afterglows at 295 degrees K. alpha (Ar2+) was found to be dependent on the power associated with the ionizing pulse initiating the discharge, the value increasing from 4.7*10-7 cm3 s-1 to 12.6*10-7 cm3 s-1 as the power was decreased. Measurements of alpha (O2+) in the argon-oxygen afterglow yielded a value of (2.1+or-0.3)*10-7 cm3 s-1 in good agreement with those values obtained by other workers using independent techniques.