ISSN print edition: 0366-6352
ISSN electronic edition: 1336-9075
Registr. No.: MK SR 9/7

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Radical reactions in the cold microwave plasma of atomized gases studied by continuous ESR flow technique

A. Tkáč

Department of Physical Chemistry, Faculty of Chemical Technology, Slovak Technical University, CS-81237 Bratislava


Abstract: Diatomic gases of H2, N2, O2 under reduced pressure and volatilized molecules of H2O, D2O, H2O2, NH3, are effectively dissociated to their atoms, when they are exposed to microwave radiation of the frequency 2450 MHz. The formed paramagnetic species H., D., .N., .O. are proved directly in the cold plasma by means of the identified ESR spectra. At constant power of the microwave transmitter (5 to 100 W) the highest spin concentration of atomized gases 2 x 1016-3 x 1016 spin cm-3 is reached in the vacuum interval of 100 up to 200 Pa. With increased pressure the atomized species gradually disappear in the consequence of recombination. In the homogeneous magnetic field of the ESR spectrometer using the TE102 mode cavity in the flowing cold plasma the secondary products of radical recombination as HO., HOO., DO. or DOO. were under the detectable sensitivity level. Nevertheless, their presence and the effect of the applied magnetic field on gas phase radical reactions were ascertained by introducing the spin-trapping technique transforming the primary instable radicals of the plasma to stable nitroxy spin-adducts of DMPO (5,5-dimethyl-1-pyrroline N-oxide). The concentration relation between the highly reactive HO. and HOO. radicals as products of the reaction .O.+HOH→ 2HO. was measured after freezing the radicals from the flowing plasma on the internal cryostat situated in the ESR cell and cooled with liquid nitrogen.Elaborating a cross-flow experimental arrangement, the kinetics of the rapid reactions between the colliding atomized gases with different molecules when introduced into the ESR cell from the opposite direction to the plasma flow were observed. The reactivity of atomized oxygen with solid targets was measured directly in the ESR cavity. In this way the one-electron transfer from the chelated transition metal cobalt(II) 3d7 to atomized oxygen forming the complex Co3+O.- was proved. Atomized oxygen can initiate surface cross-linking after its addition to a double bond in contact with exposed films of natural rubber or polyisoprene.

Full paper in Portable Document Format: 446a737.pdf


Chemical Papers 44 (6) 737–768 (1990)

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