Infrared Spectra of CH₃−CrH, CH₃−WH, CH₂WH₂, and CH⋮WH₃ Formed by Activation of CH₄ with Cr and W Atoms

Laser-ablated W atoms react with CH₄ in excess argon to form the CH₃−WH, CH₂WH₂, and CH⋮WH₃ molecules with increasing yield in this order of product stability. These molecules are identified from matrix infrared spectra by isotopic substitution. Tungsten methylidene and methylidyne hydride molecules are reversibly interconverted by α-H transfers upon visible and ultraviolet irradiations. Matrix infrared spectra and DFT/B3LYP calculations show that CH⋮WH₃ is a stable molecule with C_3v symmetry, but other levels of theory were required to describe agostic distortion for CH₂WH₂. Analogous reactions with Cr gave only CH₃−CrH, which is calculated to be by far the most stable product.