The counter ratio method has been used to investigate neutron thresholds in the (d,n) reactions on B 10 , B 11 , C 12 , and C 13 . Thresholds were found corresponding to excited states in C 11 * at 8. 107, 8.430, and 8.660 Mev; in C 12 * at 15.100 Mev; in N 13 * at 2.37 Mev; and in N 14 * at 5.683 Mev. Resonances in the reaction C l2 (d,n) were found at 3.01 and 3.36 Mev and in the reaction C lz (d,n) at 1.80, 2.45, and 3.46 Mev. The absolute cross sections for the reactions B 10 (d,n), B n (d,n), and C 13 (d,n) were measured.

The role of electronically excited singlet ('A8) oxygen molecules in the photooxidation of polymers has received increased attention in recent years. Little information regarding the interaction of ultraviolet stabilizers with singlet oxygen is known, however. In this study, singlet oxygen was produced by a microwave discharge in a flow system and rate constants were obtained for quenching by ultraviolet stabhers. It was found that some nickel chelate stabilizers are effective quenchers of singlet oxygen and their quenching behaviors can be correlated with ultraviolet stabilization effectiveness in thin polypropylene and polyethylene films. The best singlet oxygen quenchers of those examined are nickel chelatea with sulfur donor ligands.

The infrared spectrum of the solid benzene—Br2 complex has been measured to give the changes in frequency and an estimate of the changes in intensity from the pure benzene and pure Br2 crystals. The complex was usually prepared by condensing a 1:1 mixture of benzene and bromine vapor onto a cold plate, but other techniques were also tried, and partial studies are reported. These spectra show definitely that neither the benzene nor bromine molecules in our samples are located on a site possessing a center of symmetry. From the analysis of the spectrum of the complexed benzene, a site symmetry of C3v is deduced. This apparent contradiction of the results of the x-ray studies of Strømme and Hassel is discussed and reconciled. The frequency shifts and intensity changes on complex formation are discussed in some detail.

The excited-singlet and triplet-state quenching properties of ultraviolet stabilizers have been investigated using the ketone photosensitized cis-trans isomerization of piperylene in solution as the energy transfer system. Both benzophenone and 4-methyl-2-pentanone were used as photosensitizers. Nickel chelate stabilizers, particularly nickel dibutyldithiocarbamate, were found to quench singlet and triplet states by a diffusional exchange energy transfer process. The excited carbonyl quenching rate constants of metal chelates can be roughly correlated with stabilization effectiveness in thin polypropylene and polyethylene films; however, evidence is presented which questions whether the principal action of the metal chelates in the polymer involves only excited carbonyl quenching. The possibility of quenching electronically excited singlet oxygen in the polymer by metal chelates is discussed. Three organic stabilizers, a hydroxybenzophenone and two hydroxyphenylbenzotriazoles, were also examined and found to be effective quenchers of the excited states of 4-methyl-2-pentanone. In order to correlate these results with the behavior in polyolefins, mechanisms involving steric hindrance to energy transfer in the polymer and generation of singlet oxygen by the stabilizers are proposed and discussed.

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