Influence of molecular oxygen on iodine atoms production in an RF discharge

Abstract

The results of the experiments and modeling of CH3I dissociation in a 40 MHz RF discharge plasma are presented. A discharge chamber of an original design, consisting of quartz tubes between two planar electrodes, permitted us to produce iodine atoms with a number density up to 2 × 1016 cm−3. In this discharge chamber, contrary to the previous experiments with a DC discharge and RF discharge with bare planar electrodes, contamination of the walls of the tubes did not disturb discharge stability, thus increasing iodine production rate. A substantial increase in CH3I dissociation efficiency due to the addition of oxygen into Ar(He) : CH3I mixtures was observed. Complete CH3I dissociation in the Ar : CH3I : O2 mixture occurred at 200 W discharge power, while a fraction of discharge power spent on iodine atoms production at 0.17 mmol s−1 CH3I flow rate amounted to 16%. Extensive numerical modeling showed satisfactory agreement with the experiments and permitted us to estimate a previously unknown rate of constants for the processes: Ar* + CH2I2 → Ar + CH2 + I + I – 1.5 × 10−11 cm3 s−1; Ar* + CH2I2 → Ar + CH2I+ + I + e – 10−11 cm3 s−1. Also, the cross section for the process CH2I2 + e → CH2 + I + I + e was estimated to be five times smaller than for the analogous process with CH3I.