In Ag-loaded NaA zeolite the silver hydroxymethyl radical ((AgCH2OD)-C-.)(+) was stabilized and studied with electron spin echo envelope modulation (ESEEM) spectroscopy. Careful control of the CH3OD concentration enabled the measurement of ESEEM spectra from which the hyperfine and quadrupole parameters of the intramolecular hydroxyl deuterium nucleus could be estimated. The isotropic hyperfine splitting constant, A(iso), is equal to +2.9 MHz, the electron-deuteron dipolar coupling parameter T (T = g(e) beta(e)g(D) beta(D)/(hr(3))) is equal to +1.4 MHz, and the quadrupole parameter P (P = e(2)qQ/(4h)) is equal to +/- 0.12 MHz. These data are compared to listed data for the (CH2OH)-C-. radical. The differences can be interpreted in terms of electronic, electrostatic, and matrix effects.