EPR Studies of Multiple Ag Trapping Sites Produced in Gamma-Irradiated Frozen AgNO3 Ices

Abstract
EPR studies show that gamma‐irradiated AgNO3–KF and AgNO3 ices at 77°K form Ag0 in several magnetically distinct sites. Temperature and optical excitation cause conversions among these sites with little loss of Ag0. From 77 to 150°K the predominant change is form a matrix site characterized by a symmetric electric field to a matrix site characterized by an asymmetric electric field. This is explained in terms of water dipole rotation in response to the removal of the electric field of Ag+ upon formation of Ag0. Then the change in electric field due to water dipole rotation semiquantitatively accounts for the change in magnetic parameters of the Ag0 sites. The activation energy for the dipole rotation process is 0.12 eV. At higher temperature Ag0 is converted to Ag2+ with an activation energy of 0.32 eV, and finally Ag2+ decays with an activation energy of ∼ 0.5 eV. These activation energies are discussed in terms of L‐defect formation and motion of the ice matrix. Optical studies show that uv light converts Ag2+ to Ag0 in a symmetric site and that visible light converts Ag0 from a symmetric to an asymmetric site and partly back to Ag2+.