Study of solvation of excess electrons in ethylene glycol/water and methyltetrahydrofuran matrices by matrix ENDOR

Abstract

Matrix proton ENDOR signals have been measured for stabilized excess electrons produced by x irradiation at 4 K in ethylene glycol/water and in 2−methyltetrahydrofuran glasses. The matrix proton ENDOR linewidths are smaller when irradiation is carried out at 77 K. The contribution to the matrix ENDOR linewidth comes principally from predominantly dipolar interactions between the unpaired electron and the surrounding matrix protons. The change in ENDOR linewidth can be interpreted as due to a slight increase in the average distance from the trapped electron to the matrix protons contributing to the matrix ENDOR line as the temperature is raised to 77 K. This is a reflection of the solvation process for the excess electron in these organic glasses. Based on a simple model, the CH bond and molecular dipoles reorient such that the negative H end of the average CH dipole moves 0.2−0.4 Å further away from the unpaired electron as solvation becomes more complete at higher temperature. These results are consistent with the change in electron solvation implied by irreversible changes upon warming of the optical absorption spectra and the EPR linewidths of excess electrons generated at 4 K in these matrices.