Bromine reactions activated by 79Br(n,7)80Br, 81Br(n,7)82Brm + 82Br, and 82Brm(I.T.)82Br nuclear transformations were studied in halomethanes as functions of mole fraction of Br2, phase, density, and intermolecular distance. Gas phase systematics coupled with the density and mole fraction of Br2 studies demonstrate the existence of systematic trends in the condensed phases as evidenced by the Richardson-Wolfgang effect. A definitive difference due to activation that is independent of system and suggests the importance of caging at higher densities is shown by the variation of total and individual organic product yields with density. The study of total organic product yield vs. intermolecular distance provides both a means of separating cage and molecular reactions and suggests the importance of molecular properties in the caging event.

Publication costs assisted by the U.S. Energy Research and Development AdminlstratlonThe reactions of lZsI activated by radiative neutron capture with acetylene occur primarily through an addition channel forming an electronically excited reaction intermediate. Acetylene is unlike olefins in that no photochemical addition occurs under conditions simulating sample handling. In an excess of gaseous acetylene, at l atm 14.9 f 0.6% of lZsI is stabilized as organic activity to the following extent: CH3I 0.49%, CH& 0.70%; C2H31 0.40%, CzH5I 9.30%; i-C3H7I 2.71%; CH~CH~CHICHS 1.10%, CH3(CH2)3I 0.20%. The effects of rare gas additives in moderating lZ8I with gaseous CzH2 were determined in an effort to ascertain the nature of the activation process. Only the C2H51281 yield is decreased by the presence of rare gases, suggesting that both hot lZsI ions and thermal I+(lD2) and other excited ions are involved in the primary addition to acetylene. The gas to condensed phase studies showed a depletion of all C1, vinyl iodide, Cs, and C4 128I-labeled products; where the only product observed in high pressure gas and condensed phase systems was C2H51281. A reaction scheme is proposed which postulates the existence of an excited complex reaction intermediate. The properties of the proposed complex are compared qualitatively to those predicted by RRKM, "caged" complex, and caging radical theories of enhancement yields.

The dispersion coefficient (D) Is the most popular peak descriptor In flow Injection analysis (FIA). Yet this concept of

In the presence of a large excess of gaseous methane, 54.4±0.5% of p28 formed by (n, 'Y) activation was found to become stabilized in organic combination. The effects of inert-gas additives in moderating the reaction of Il28 with CH. were determined in an effort to ascertain the mechanism. The data, extrapolated to zero mole-fraction methane, indicate that xenon is capable of reducing the organic 1 128 to 11% whereas neon, argon, and krypton each reduce it to only about 36%. These data suggest that of the 54.4% organic P.28, about 18.4% forms as a result of hot 11.28 reactions, 11% as a result of excited iodine atoms or 1+ ions in the ap 2 , aPI, and/or apo states, and 25% as a result of reactions of 1+ (lD2) ions.

It was found in a systematic study of 128I reactions activated by radiative neutron capture in various gaseous halomethanes that the formation of 128I-labeled organic products proceeds entirely by hot (requiring excess kinetic energy to occur) reactions. This is unlike the reactions of 128I with CH4 where the organic product CH8128I was formed not only by hot 128I atoms but by thermal ion-molecule reactions involving 1+ in the 'D2, 8P0, 8Pi, and 3P2 states. In the various halomethane systems only two 128I-labeled organic products were found, those resulting from halogen and hydrogen substitution. The limiting 128I organic yields in gaseous CH3F, CHgCl, CHjBr, and CH3I were 11.2, 4.2, 0.67, and 0.20%, respectively. The kinetic energy spectra for (n, 7)-activated 128I atoms or ions were calculated and the results showed that an appreciable fraction of the 128I species are bom with low kinetic energies, in or near the reactive zone. The only physical or chemical parameter that explained the trend in organic yields was the energy degradation factor of the halomethane system, correlating well with the kinetic energy spectrum of 128I.