The solvation of excess electrons in fluid methane and ethane is studied by path integral Monte Carlo computer simulation and by the fast-Fourier-transform-Lanczos diagonalization method using a newly developed electron-alkane pseudopotential. Many-body polarization interactions between solvent molecules are treated using a mean field approximation in the simulation. In methane, it is found that the electron is in an extended state throughout the whole fluid density range studied. In ethane, it

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... is found that the solvated electron gradually becomes localized or "self-trapped," with cavity formation occurring at a fluid density where experimentally the electron is found to have a very low mobility and the threshold value for electron photoconduction rises above zero. The electronic ground state energies in the unperturbed solvent and in the electron-equilibrated solvent were compared. At the same density these electronic energies are very close to each other in methane and in the low density ethane fluids, but at higher ethane densities, where cavity formation takes place, the ground state energy in the electron solvated fluid is lower than that in the unperturbed fluid. 9054