The reactions of gas-phase atomic hydrogen [H(g)] and deuterium [D(g)] with preadsorbed nitric oxide [NO(a)] on the hexagonally close-packed Ru(001) surface have been studied by means of temperature-programmed desorption and high-resolution electron energy loss spectroscopy (HREELS). Exposure of gas-phase atomic deuterium to the saturated NO overlayer at a surface temperature of 100 K results in the observation of N2O, D2O, D-2, NO, N-2, and O-2 in subsequent thermal desorption spectra. Since D2O is formed at low surface temperatures, an Eley-Rideal-like mechanism in which deuterium atoms from the gas phase react with the oxygen end of the preadsorbed NO is suggested. Spectroscopic evidence for this reaction on the Ru(001) surface is provided by HREEL spectra which show vibrations at 983 cm(-1) [after H(g) exposure] and 977 cm(-1) [after D(g)]. Since the loss at 983 cm-1 has not shifted significantly upon deuterium substitution, these losses are assigned to weakened N-O stretches of NOH (NOD) species. These species are stable after annealing to 200 K on Ru(001).