The rate constants for attachment of excess electrons to 1,3-butadiene (k(a)) and detachment from the butadiene anion (k(d)) in n-hexane are reported. The equilibrium constant, K-eq = k(a)/k(d), increases rapidly with pressure and decreases the temperature increases. At -7 degrees C attachment is observed at 1 bar. At high pressures the attachment rate is diffusion controlled. The activation energy for detachment is about 21 kcal/mol; detachment is facilitated by the large entropy of activation. The reaction volumes for attachment range from -181 cm(3)/mol at 400 bar to -122 cm(3)/mol at 1500 bar and are largely attributed to the electrostriction volume of the butadiene anion (Delta (V) over bar(el)). Values of Delta (V) over bar(el) calculated by a model, which includes a glassy shell of solvent molecules around the ion, are in agreement with experimental reaction volumes. The analysis indicates the partial molar volume of the electron in hexane is small and probably negative. It is shown that the entropies of reaction ace closely related to the partial molar volumes of reaction.