We report on the properties of Si diffused with molybdenum (Mo) investigated using experimental techniques that included Fourier transform deep-level transient spectroscopy (FT-DLTS) and scanning infrared microscopy (SIRM). Samples were prepared using boron-doped float zone (100)Si wafers (100-400 Omega cm) and Mo was diffused into them by placing Mo powder onto the Si surface and annealing in a vacuum (8 x 10(-6) Torr) at temperatures between 400 and 800 degrees C for 1-10 h. FT-DLTS measurements revealed that deep levels due to Mo (E-v + 0.29 eV) were only formed in samples when Mo was diffused above a threshold temperature of 650 degrees C. SIRM imaging showed the presence of Mo-related precipitates having a density of 2.3 x 10(7)-5.8 x 10(9) cm(-3) near the surface region and iron-related precipitates having a density of 1.2 x 10(7)-1.1 x 10(8) at a depth of 30 mu m. The precipitate size was found to be strongly dependent on diffusion temperature and ranged between 50 and 100 nm as calculated from the scattered light intensity. The minority carrier lifetime was found to decrease with increasing density of iron traps that were unintentionally incorporated during the diffusion process.