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

• Published in: Plasma sources science & technology 2016-06, Vol.25 (3), p.35027
• Main Authors: Mikheyev, P A, Ufimtsev, N I, Demyanov, A V, Kochetov, I V, Azyazov, V N, Napartovich, A P
• Format: Article
• Language: English
• Subjects: iodine atoms; methyl iodide dissociation; oxygen-iodine laser; plasma chemistry; RF discharge
• ISSN: 0963-0252; 1361-6595
• DOI: 10.1088/0963-0252/25/3/035027

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.