A global adiabatic potential energy surface (PES) corresponding to the second singlet state 1¹A″ (1¹B₁) of CH₂ has been computed in a similar way as the first singlet state 1¹A′ in our previous work [B. Bussery-Honvault et al., J. Chem. Phys., 2001, 115, 10701]. This PES has a calculated well depth of 79.9 kcal mol⁻¹ relative to the C(¹D) + H₂ asymptote and correlates to CH(²Π) + H. It presents large barriers in the C(¹D) + H₂ arrangement for both collinear and perpendicular geometries but no barrier for geometries about 60° and leads to a sideways insertion mechanism for the reaction C(¹D) + H₂ → CH(²Π) + H. The ab initio calculations were carried out for 4644 geometries and the resulting energies were fitted to a many-body expansion. Accurate three-dimensional quantum mechanical scattering calculations have been performed for the C(¹D) + H₂(v = 0, j = 0) reaction on this ab initio 1¹A″ PES in the collision energy range [0–11.5 kcal mol⁻¹]. The J = 0 reaction probabilities show dense resonance structures as those obtained with the 1¹A′ PES. However some different dynamical features have been found.