Production of iodine atoms by RF discharge decomposition of CF₃I

Abstract

A generation of atomic iodine by dissociation of CF 3 I in RF discharge was studied experimentally in a configuration ready for direct use of the method in the oxygen-iodine laser. The discharge was ignited between the coaxial electrodes with a radial distance of 3.5 mm in a flowing mixture of 0.1-0.9 mmol.s -1 of CF 3 I and 0.5-6 mmol.s -1 of buffer gas (Ar, He) at a pressure of 2-3 kPa. The discharge stability was improved by different approaches so that the discharge could be operated up to a RF source limit of 500 W without sparking. The gas leaving the discharge was injected to the subsonic or supersonic flow of N 2 and concentration of generated atomic iodine and gas temperature were measured downstream of the injection. An inhomogeneous distribution of the produced iodine atoms among the injector exit holes was observed, which was attributed to a different gas residence time corresponding to each hole. The dissociation fraction was better with pure argon as a diluting gas than in the mixture of Ar-He, although the variation in the Ar flow rate had no significant effect on the CF 3 I dissociation. The dissociation fraction calculated from the atomic iodine concentration measured several centimeters downstream of the injection was in the range of 7 to 30% when the absorbed electric energy ranged from 200 to 4000 J per 1 mmol of CF 3 I. Corresponding values of the fraction of power spent on the dissociation decreased from 8 to 2%.% and the energy cost for one iodine atom increased from 30 to 130 eV. Due to a possible high rate of the atomic iodine loss by recombination after leaving the discharge, these values are considered as lower limits of those achieved in the discharge.

Experimental and theoretical study of RF capacitively coupled plasma in Ar–CF4–CF3I mixtures

“…CF 3 I-containing plasma was also applied for etching of usual SiO 2 dielectric as a low-global-warming-potential plasma [13], for charging-damage-free dielectric etching in pulsed plasma [14] and also for iodine atom production in the chemical oxygen-iodine laser problem [15,16].…”

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

“…Glow discharges had proved to be suitable for atomic iodine production out of different precursor molecules both in dc and pulsed regimes [3][4][5][6][7]. An advantage of using precursors instead of molecular iodine is a small fraction of I 2 at the discharge generator outlet, because it is formed in discharge plasma only through the recombination of iodine atoms.…”

Heterogeneous losses of externally generated I atoms for OIL

“…Electric-discharge [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] and chemical [18][19][20] generators have been proposed as a source of iodine atoms for the use in OIL. Dissociation of iodine-containing molecules in electric-discharge plasmas had been proved to be useful for external production of iodine atoms.…”