The addition reaction of chlorine with ethylene (C 2 H 4 ) is expected to proceed via a free radical intermediate, the 2-chloroethyl radical, however, this intermediate has not been previously observed spectroscopically. Irradiation at 365 nm of a co-deposited mixture of Cl 2 , C 2 H 4 , and p-H 2 at 3.2 K produces a series of new lines in the infrared spectrum. A strong line at 664.0 cm -1 and weaker lines at 562.1, 1069.9, 1228.0, 3041.1 and 3129.3 cm -1 are concluded to be due to a single carrier based on their behavior upon subsequent annealing to 4.5 K and secondary irradiation at 254 and 214 nm. The positions and intensities of these lines agree with the MP2/aug-cc-pVDZ predicted vibrational spectrum of the 2-chloroethyl (CH 2 CH 2 Cl) radical. In order to confirm this assignment, isotopic experiments were performed with C 2 D 4 and t-C 2 H 2 D 2 and the corresponding infrared bands due to the deuterium isotopomers of this radical (CD 2 CD 2 Cl and C 2 H 2 D 2 Cl) have been observed. A final set of experiments were performed following irradiation of the Cl 2 /C 2 H 4 /p-H 2 mixture at 365 nm, in which the matrix was irradiated with filtered infrared light from a globar source, which has been shown to induce reactions between isolated Cl atoms and matrix H 2 to produce HCl and H atoms. In these experiments, the major products observed were HCl, the ethyl radical (C 2 H 5 ) and ethyl chloride (C 2 H 5 Cl) and the possible mechanisms for the formation of these species are discussed.