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From 166th American Chemical Society national meeting; Chicago, Illinois, USA (26 Aug 1973). Rate constants for the interaction of ortho- positronium atoms with a series of diamagnetic organic compounds were determined. Nitrated aromatic molecules interact far more readily with orthopositronium than do nitrated aliphatic molecules. The observed rate constants for the aromatic molecules show a distinct dependency on the nature of the subsitituents and their relative positions in the aromatic ring. This dependency may be attributed to steiic interactions which influence the relative electron charge density on the atoms in the molecule and alter the molecular energy levels. (auth)

From 7th international hot atom chemistry symposium; Julich, F. R. Germany (10 Sep 1973). The stereochemistry of the halogen for halogen substitution at asymmetric carbon atoms, induced by energetic or thermal bromine and iodine species was studied in diastereomeric alkyl halide molecules such as d,1- and meso-2,3-dichlorobutane. Energetic /sup 80/Br species were generated via the /sup 80m/Br (I.T.)/sup 80/Br nuclear process in reactor produced CF/sub 3/ /sup 80m/Br and allowed to react with the substrate molecules while still possessing excess kinetic energy or after having become thermalized in collisions with argon atoms. /sup 125/I species were produced via the radioactive decay of / sup 125/Xe. The observed results show in unmoderated systems generally a predominance of those products which were formed in the halogen for halogen exchange process under retention of configuration. (auth)