Methane activation by laser-ablated Th atoms on the triplet potential energy surface produces the methylthorium hydride, CH3-Th-H, that converts smoothly by alpha-H transfer to CH2-ThH2, which relaxes in the matrix to the more stable singlet methylidene, CH2-ThH2. This first actinide methylidene was characterized from argon matrix infrared spectra and B3LYP calculations in our laboratory. We now report neon matrix investigations, which include the methylthorium hydride and the Th-D stretching modes of CD2=ThD2 that are blue-shifted in neon from under the intense CD4 precursor absorption, and reactions with CH2D2 that give rise to the CHD-ThHD modifications and their alpha-H and alpha-D transfer counterparts CD2=ThH2 and CH2=ThD2. New intrinsic reaction coordinate calculations show that this reaction proceeds smoothly on the triplet potential energy surface.