Molecular complex formation between positronium and organic molecules in solutions

Abstract

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.

Current Problems and Unknowns in Positronium Dynamics

“…(9). The authors underline that the slope of the ln(k ) vs. 1/T variation at low T provides an activation energy close to E η .…”

“…Nitrocompounds have soon been recognised to promote the specific reaction of bound-state formation with Ps [9]. A particular feature of this reaction lies in its reversibility, as revealed by the fact that k , derived from the data by using Eq.…”

“…A particular feature of this reaction lies in its reversibility, as revealed by the fact that k , derived from the data by using Eq. (2), shows a maximum when studied as a function of temperature (T ); the first reaction scheme proposed was thus as follows [9]:…”

“…A typical example is shown in Fig. 2, for nitrobenzene in toluene [9]. In a conventional approach, k 1 should obey Eq.…”

“…(2), with 1/T . Experimental data (•) for nitrobenzene in toluene selected from [9]. Calculated values ( ) from a fit by using Eqs.…”