Physico-Chemical nanomaterials science

Decomposition of methane in Ar-CH4 clusters

Doronin Yu. S., Tkachenko A. A., Vakula V. V., Kamarchuk G.V.

B.Verkin Institute for Low Temperature Physics and Engineering of the NAS of Ukraine,47 Nauky Ave., Kharkiv 61103, Ukraine.
E-mail: doronin@ilt.kharkov.ua

	For the first time, the dissociation of methane molecules embedded in argon clusters has been investigated. Two-component Ar-CH4 clusters containing approximately 1000 atoms (molecules) in a cluster with a temperature of about 40 K were formed in a supersonic gas jet exhausting into a vacuum. The concentration of methane in the original gas mixture was varied from 0.1 to 0.5 percent. Clusters were excited by electrons with energy of 1 keV and 20 mA current. The Ar-CH4 cathodoluminescence spectra were recorded within the 6.5-10.5 eV range. A complete radiation extinguishing of argon centers (Ar4+)*, Ar2* and the appearance of the Ly-a (1215,7 Å) atomic hydrogen line have been detected, indicating that there are cryochemical reactions of CH4 dissociation in the clusters originating from the interaction of impurity methane with the matrix's hole carriers. 
	The sequence of reactions leading to the emission of Ly-a Ar-CH4 clusters has been studied. As a result of solvation, a multi-atomic ion molecule H+ArN(v) is formed consisting of a proton with argon atoms stuck to it. Since the preceding reactions are exothermic, this molecule is in a vibrational-excited state (v) and the process of its dissociative recombination with an electron from the conduction band can lead to the settlement of the atomic level of the excited hydrogen atom. 
	The effective deprotonation found in Ar-CH4 clusters makes it possible to solve the problems of proton accumulation in inert cryomatrices in the future and to investigate the chemical reactions of hydrogen ions with frozen impurities. 

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