Evidence is presented which supports the reversible formation of molecular complexes between Ps atoms and a series of nitrobenzene derivatives and p-benzoquinone in solution. The activation energy for the forward reaction step I (Ps + (II) *=* PsM (I)) is generally very small. EA ~1 kcal/mol. AH eq, the enthalpy of the overall process, ranges from almost zero, in the case of very unreactive substrates, such as toluene or heptane, to -8 kcal/mol for dinitrobenzene or p-benzoquinone. The reactivities of the various substrate molecules toward Ps follow trends as observed in conventional molecular complex formation. Furthermore an attempt has been made to assess the role of the solvent upon the stability of the molecular complexes.
Madia, Schug, Nichols, and Ache (8) See paragraph at end of text regarding supplementary material. (9) We noted a misprint in the 3T2 electrostatic matrix of Sugano, Tanabe, and Kamlmura_(ref 6a). The (t23(2Ti)e3T2l|t2e3 3T2) matrix element should be -V6B. It is correctly listed in an earlier paper of Tanabe and•
Rate constants for the interaction of ortho-positronium atoms with a series of diamagnetic organic compounds have been determined. Nitrated aromatic molecules interact far more readily with ortho-positronium 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 steric interactions which influence the relative electron charge density on the atoms in the molecule and alter the molecular energy levels.
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