Photoemission cross sections (a,,) for the A-X, B-X, and C-X bands of CH resulting from the He(2 S-3) + CH(3)X (X = H, Cl, Br, I) reaction have been studied in the relative collision energy (E(R)) of 120-210 meV. Formation cross sections (sigma) for CH(A, B, C) were evaluated from the sigma(em)’s taking account of predissociation : A good correlation was found between the sum of the sigma’s for CH and the dipole-induced dipole interaction of He(2 S-3) with targets. The sigma(em)’s from methane increase with E(R), while those from methyl halides decrease with increasing E(R). The positive energy dependence for methane implies that effective potentials leading to CH are repulsive, whereas attractive potentials play a dominant role in the reaction of He(2 S-3) With methyl halides. Model potentials between CH3Cl and He*(Li) calculated using ab initio molecular orbital methods indicate that He(2 S-3) approaches CH3Cl not from CH3 side but from Cl side.