EPR OF SILVER-AMMONIA ADDUCTS IN GAMMA-IRRADIATED AGNA-A ZEOLITE WITHLOW SILVER CONTENT

An EPR study has been performed on a low Ag+-exchanged Na-A zeolite (A g0.1Na11.9-A) on which ammonia had been adsorbed followed by exposure to gamma-radiation at 77 K. The formation of Ag atoms, normally observ ed for zeolites with a high Ag content, is abated by the presence of a mmonia. New EPR spectra with the silver hyperfine coupling constant sl ightly smaller than that of isolated silver atoms were observed. The n ew spectra were assigned to two silver-ammonia complexes, [Ag-NH3](0) and [Ag-(NH3)(2)](0), the former being more thermally stable than the latter; the latter decayed at 150 K. The EPR parameters of [Ag-NH3](0) were determined as follows: g(iso) = 2.005 and a(iso)(Ag-107) = 38.0, A(perpendicular to)(N-14) = 1.4, A(parallel to)(N-14) = 1.7 and a(iso )(H-1) approximate to 0 mT. The formation reactions and possible locat ions of the adduct radical are discussed in terms of annealing tempera tures and the amount of ammonia introduced.