The coordination process of C2H4 Onto "naked" coordinatively bisunsaturated tungsten carbonyl, W(CO)(4) being prepared by pulsed 266-nm laser photolysis of W(CO)(6), was observed by a time-resolved infrared absorption spectroscopy. W(CO)(4) reacted with C2H4 to form W(CO)(4)(eta(2)-C2H4). The nascent W(CO)(4)(eta(2)-C2H4)* had an absorption band with a broad tail to longer wavelength assignable to equatorial CO vibrational mode at 1926 cm(-1) while another band assignable to axial CO vibrational mode at 1977 cm(-1) seemed to be narrower. W(CO)(4)(eta(2)-C2H4) reacted consecutively with C2H4 to make a simple coordination complex cis-W(CO)(4)(eta(2)-C2H4)(2) with two bands at about 1933 cm(-1) (B-2 mode) and 1981 cm(-1) (Al and BI modes overlap) in the observation region of 1880-2035 cm(-1). The assignment of the absorption spectra of these complexes is based on the kinetics and stoichiometry of the transient species and on the comparison with the IR spectra previously reported for metal-olefin complexes. The bimolecular rate constants were estimated to be (3.0 +/- 0.6) x 10(6) Torr(-1) s(-1) for W(CO)(4) + C2H4 and (0.7 +/- 0.1) x 10(6) Torr(-1) s(-1) for W(CO)(4)(eta(2)-C2H4) + C2H4 at 5.5 Ton total pressure with balance Ar at room temperature.