Reaction of laser-ablated Zr with CH4 ((CH4)-C-13, CD4, and CH2D2) in excess neon during condensation at 5 K forms CH2=ZrH2, the simplest alkylidene hydride complex, which is identified by infrared absorptions at 1581.0, 1546.2, 757.0, and 634.5 cm(-1). Density functional theory electronic structure calculations using a large basis set with polarization functions predict a C, symmetry structure with agostic C-H---Zr bonding and distance of 2.300 Angstrom. Identification of the agostic CH2=ZrH2 methylidene complex is confirmed by an excellent match of calculated and observed isotopic frequencies particularly for the four unique CHD=ZrHD isotopic modifications. The analogous reactions in excess argon give two persistent photoreversible matrix configurations for CH2=ZrH2. Finally, methane activation by CH2=ZrH2 gives the new (CH3)(2)ZrH2 molecule.