Picosecond time-resolved infrared spectroscopy has been used to investigate the primary UV photochemistry of [CpFe(CO)(2)](2) (Cp=eta(5)-C5H5) in alkane solution at room temperature. We show that the triply bridged intermediate, CpFe(mu-CO)(3)FeCp, is formed within 10 ps. We observe a new intermediate with a v(CO) band at 1908 cm(-1) that reacts at a diffusion-controlled rate (k=(1.3+/-1.0) (2 sigma) x 10(10) s(-1)) with THF to form Cp(CO)Fe(mu-CO)(2)Fe(THF)Cp.