Reactions of fluorine-18 atoms with ethylene

Abstract

Publication costs assisted by Division of Research, U. S. Atomic Energy Commission Energetic 18F atoms formed by the 19F(n,2n) 1SF nuclear reaction can undergo both hot and thermal addition reactions with ethylene to form excited CH218FCH2* radicals. The hot reactions of 18F can be almost entirely suppressed by moderation with SF6 or CF4, and the excited CH218FCH2* radicals exhibit normal stabilizationdecomposition (to CH18F=CH2 + H) behavior vs. pressure for monoenergetically excited radicals. The stabilized radicals are observed as CH3CH218F after reaction with scavenger HI. The half-stabilization pressures for SF« and CF4 are 80 and 135 Torr, respectively, and are essentially unchanged for moderator fractions >0.75. The difference in half-stabilization pressures indicates that SF6 is more efficient, per molecule. in removing the excitation energy of CH2,SFCH2* radicals. In less-moderated systems, hot reactions are also observed: (a) the formation of CH18F=CH2 by a more energetic route; (b) the formation of CH18F from secondary decomposition of CH18F=CH2; and (c) the formation of CH218F by decomposition of CH2-18FCH2*. The rupture of the C-C bond in CH218FCH2* probably occurs predominantly after capture of 18F at high-impact parameters with consequent high-angular momentum in the excited radical. Similarly, substitution of 1SF/H at high-impact parameters is postulated to lead to the C=C bond rupture in CH18F=CH2*.

Hydrogen atom abstraction by fluorine atoms

“…With SFg in such excess, each 18F atom is >9 times more likely at each energy to make a nonreactive collision with SFg than to make a possibly reactive collision with C2H2 or HI, Under such conditions, most 18F atoms are essentially thermal in kinetic energy at the time of reactive collision. [18][19] The straight line of Figure 1 is a reasonable fit to these data, leading to an estimate from its slope of 0.37 :fc 0.05 for the ratio of the rate of abstraction from HI vs. addition to C2H2.…”

Spectroscopic studies of some laser dyes

“…carried out which unambiguously involve the reactions of atomic fluorine with aromatic systems despite the considerable interest in such reactions.2 345However, radioactive 1SF atoms (tv, = 110 min) can be produced by various nuclear reactions, including the 19F(n,2n)18F reaction with fast neutrons, and these atoms can be brought to thermal energies without bond formation by multiple collisions with suitable inert moderators. [3][4][5][6][7][8][9][10][11][12][13][14][15] In the last several years, research in this laboratory has utilized such thermal 18F atoms for reaction studies with olefins,6•7•9•10 acetylene,8 various RH compounds,11 and a variety of inorganic species.12•13…”

Relative reaction rate involving thermal fluorine-18 atoms and thermal fluoroethyl radicals with oxygen, nitric oxide, sulfur dioxide, nitrogen, carbon monoxide, and hydrogen iodide

“…Thermal 18F atoms are readily produced through fast neutron irradiation of SFe, by the 19F(n,2n)18F nuclear reaction, followed by nonreactive moderating collisions with other molecules of SFe•2"7 When other components of a gaseous mixture with SFe are restricted to total mole fractions <0.05, essentially all (>97%) of the 18F atoms react with thermal kinetic energy. 6 In the presence of C2H2 or C2H4, approximately 857 and 60%,6 respectively, of such 18F atoms react by addition to the it bond, as in (1) and (3). The fluorovinyl 18F radical formed in (1) can be readily converted to CH2=CH18F by reaction with HI as in (2) ;7 the assay of the radioactivity of CH2=CH18F is straightforward by radio gas chromatography.…”

“…The last three are all excellent scavengers for stabilized CH2CH218F radicals, and relative reaction rates were obtained for each us. the abstraction reaction 6 with HI. Carbon monoxide also exhibited a lesser scavenging ability for both CH2CH218F and CH=CH18F radicals; N2 did not react to any observable extent with CH=CH18F radicals.…”