The reactions of chlorine and hydrogen atoms with trans-1,3-butadiene in solid para-hydrogen (p-H 2) were investigated with infrared (IR) absorption spectra. When a p-H 2 matrix containing C 2 and trans-1,3-butadiene was irradiated with ultraviolet light at 365 nm, intense lines at 650.3, 809.0, 962.2, 1240.6 cm -1, and several weaker ones due to the trans-1-chloromethylallyl radical, (CH 2CHCH)CH 2Cℓ, appeared. Observed wavenumbers and relative intensities agree with the anharmonic vibrational wavenumbers and IR intensities predicted with the B3PW916-311g(2d, 2p) method. That the C atom adds primarily to the terminal carbon atom of trans-1,3-butadiene is in agreement with the path of minimum energy predicted theoretically, but in contrast to the reaction of C propene in solid p-H 2 J. Amicangelo and Y.-P. Lee, J. Phys. Chem. Lett. 1, 2956 (2010)10.1021/jz101119b in which the addition of C to the central C atom is favored, likely through steric effects in a p-H 2 matrix. A second set of lines, intense at 781.6, 957.9, 1433.6, 2968.8, 3023.5, 3107.3 cm -1, were observed when the UV-irradiated C 2trans-1,3- butadienep-H 2 matrix was further irradiated with IR light from a SiC source. These lines are assigned to the trans-1-methylallyl radical, (CH 2CHCH)CH 3, produced from reaction of 1,3-butadiene with a H atom resulted from the reaction of C atoms with solid p-H 2 exposed to IR radiation.