Condensation reactions in a microwave-induced acetylene plasma

Mass Spectrometry of Free Radicals

“…The principal ionic condensation reaction was proposed to result from the condensation of ionized acetylene C 2 H 2 + with neutral acetylene to generate the C n +2 H 2 + species, while hydrogen atoms were proposed to account for the formation of the C m H n neutral species ( n > m ). The lack of neutral and ionic species with odd-numbered carbons was interpreted by the unfavorable cleavage of acetylene to CH radicals to a significant extent, in agreement with the conclusion drawn earlier . Analysis of a dilute mixture of acetylene with nitrogen was reported later by Fujii, with the observed production of derived nitriles, amines and hydrazines.…”

“…Only xenon showed evidence for excess energy reaction. Platzner and Marcus 439 confirmed later the noninfluence of the admixture of argon in a microwave discharge in acetylene. Operating with a higher pressure value than in the preceding case (namely, ca.…”

“…The ethynyl radical was proposed as a major reactant for the condensation of the acetylene molecule to a C 4 H 2 product, which further reacts with acetylene to generate higher carbon-content neutrals. As no species with an odd number of carbon atoms were detected during the experiments, the authors concluded that radicals, or ions, with one carbon atom were not generated directly in the plasma, the microwave energy is assumed to preferentially conduct to a C−H bond breaking rather than a C⋮C triple bond breaking in accordance with the energy requirements for such dissociations . Nevertheless, this preference is altered when adding oxygen or nitrogen to the acetylene discharge.…”

“…As no species with an odd number of carbon atoms were detected during the experiments, the authors concluded that radicals, or ions, with one carbon atom were not generated directly in the plasma, the microwave energy is assumed to preferentially conduct to a C-H bond breaking rather than a CtC triple bond breaking in accordance with the energy requirements for such dissociations. 439 Nevertheless, this preference is altered when adding oxygen or nitrogen to the acetylene discharge. In the presence of oxygen and nitrogen, oxidation products and nitrogen-containing species (mainly cyanoacetylenes H(CtC) n CN) are generated in addition to polyacetylenes, and methylene or CN • radicals are presented as the major radical intermediates.…”

Controlled dust formation in pulsed rf plasmas

“…Another class of gases used for the production of particles are hydrocarbons as C 2 H 2 or CH 4 . Although some effort has been made to develop suitable reaction schemes able to predict the behavior of plasma chemical systems, [14][15][16][17][18][19][20] we are still far away from a complete understanding of low temperature plasmas in reactive gases. Reports on powder formation in hydrocarbon plasmas together with the proposed models of nucleation [20][21][22] have already been made in the 1970s.…”