Solvent clustering around pyrazine ions in the high-compressibility region of supercritical ethane

Pyrazine and methylpyrazine attach electrons reversibly in supercritical (SC) ethane in the interesting region near critical densities. Very rapid shifts in the attachment equilibrium occur over very narrow pressure ranges. Reaction volumes for electron attachment to these solutes range from -1.0 to -45 L/mol, depending on conditions. The agreement of the values of DeltaV(r) with the calculated values from the compressible continuum model is excellent, indicating that the model predicts the electrostriction volume by ions in SC ethane quite accurately, and also suggesting that the partial molar volumes of neutral pyrazine and methylpyrazine are small by comparison to that of the ions.