A. D. Britt

Bio: A. D. Britt is an academic researcher from United States Naval Research Laboratory. The author has contributed to research in topics: Reactivity (chemistry) & Adduct. The author has an hindex of 4, co-authored 6 publications receiving 51 citations.

Free Radicales of TATB

Abstract: TATB (1,3,5-triamino-2,4,6-trinitrobenzene) forms an unusually stable free radical upon irradiation with ultraviolet light. Extraction with dimethylsulfoxide yields a liquid solution ESR spectrum which is, apparently, due to a TATB-H adduct. The g-values, spectral widths, and hyperfine assignments for the solution radical are given.

Generation of Free Radicals in RDX and HMX Compositions

Abstract: Efforts to generate detectable concentrations of free radicals in explosives, binders, and their mixtures are described. Radicals were readily produced in polycaprolactone and polyethylene glycol binders at liquid nitrogen temperature using stresses as low as 0.4 kbar. These radicals were all of the peroxy type, and presumably formed by reaction of mechano-radicals with oxygen present in the polymer. No mechano-radicals were observed from HMX or RDX using samples cooled to liquid nitrogen temperature and applied stresses up to 4 kbar. In neither impacted samples that failed to explode nor the residues remaining after a partial explosion were radicals detected by ESR. Low temperature γ-irradiation of these materials was also carried out. Free radical signals originating in both the polymer and the explosive could be identified. The reactivity of NO2 radicals from γ-irradiated HMX is enhanced in the presence of binder. In γ-irradiated HMX/polycaprolactone mixtures, the NO2 radical anneals rapidly at 150 K, versus 240 K for HMX alone. Evidence is presented to suggest that the relatively stable NO2 radical (such as produced by γ-irradiation) in HMX does not play a dominant role in mechanical initiation.

Impact Sensitivity of γ-Irradiated HMX

Abstract: Impact of thin layers of HMX at room temperature and near liquid nitrogen temperature were performed. Polycrystalline powders of HMX irradiated with 7.5 megarad in evacuated tubes at liquid nitrogen temperature showed significant enhanced sensitivity. With 10-megarad irradiations of HMX in evacuated tubes at liquid nitrogen temperature frequent spontaneous explosions in HMX have occurred. ESR measurements on impacted HMX and RDX powders at room temperature and near liquid nitrogen temperature at energies of less than 1 kg · m have not produced detectable mechanically generated free radicals. A significant increase in sensitivity of vacuum irradiated HMX was observed but efforts to correlate this with the dominant frozen-in NO2 γ-radical concentration were unsuccessful. It is suggested that the NO2 radical is a chain terminating radical in explosive systems.

Ring Closure Mediated by Intramolecular Hydrogen Transfer in the Decomposition of a Push−Pull Nitroaromatic: TATB

Abstract: Using gradient-corrected density functional theory, we have investigated various competing mechanisms involved in the early stages of the decomposition of a “push−pull” (containing both electron-donating and -withdrawing groups) aromatic (1,3,5-triamino-2,4,6-trinitrobeznene, TATB), and particularly how hydrogen transfer affects the competition between ring closure and single bond scission. On the basis of the obtained energetics, we found several previously suggested mechanisms to be energetically disfavored. These mechanisms include direct N−H, N−O, C−NH2 bond dissociation, carbon ring cleavage, and the production of NO2-1 anion. Our results indicate that the rate-limiting step is ring closure mediated by intramolecular hydrogen transfer. This mechanism is predicted to have a barrier height of 47.5 kcal/mol. The hydrogen motion forms a biradical state which we suggest is the precursor to further decomposition products, such as benzofurazans.

Photophysical and photochemical properties of rhodamine 6G in alcoholic and aqueous sodium dodecylsulphate micellar solutions

Abstract: The photodecomposition of the rhodamine 6G (R6G) dye dissolved in n -alcohols and aqueous sodium dodecylsulphate (SDS) micellar solution was investigated under continuous UV-visible illumination. The results indicate that in alcohol solution the photodecomposition efficiency increases with the dye concentration. It also depends on the nature of the alcohol the lowest efficiency being observed in ethyleneglycol. The mechanism involves the electron transfer reaction of the triplet excited state with a ground state dye molecule (T + S 0 → R + + R − . In aqueous SDS micellar solution, the R6G cation is embedded in the hydrophobic interior of the micelle close to the negatively charged sulphate end groups. We show that a rather high concentration (3 × 10 −3 M) of R6G can be dissolved in 10 −1 M SDS aqueous solution, protecting R6G from the electron transfer reaction and secondary decomposition reactions.