The mobilities of several radical cations and anions are measured in n-hexane using a thin-sheet time-of-flight (TOF) technique. We observe the radical cations of N,N,N,N’-tetramethyl-p-phenylenediamine, zinc tetraphenylporphine, and pyrene and the radical anions of perfluorobenzene, p-benzoquinone, anthraquinone, chloranil, buckminsterfullerene (C-60), and octafluoronaphthalene : For all electron accepters but C-60,, the dependence of the anionic TOF on acceptor concentration reveals the:appearance of the homodimer radical anion at sufficiently high concentrations. The equilibrium constant for the monomer anion/monomer acceptor association reaction is obtained from the concentration studies. A Born-Haber cycle is then applied to estimate the difference between the electron affinities of the monomer and dimer molecules in the gas phase.