Tungsten Hydride Phosphorus- and Arsenic-Bearing Molecules with Double and Triple W-P and W-As Bonds

Laser ablation of tungsten metal provides W atoms which react with phosphine and arsine during condensation in excess argon and neon, leading to major new infrared (IR) absorptions. Annealing, UV irradiation, and deuterium substitution experiments coupled with electronic structure calculations at the density functional theory level led to the assignment of the observed IR absorptions to the E≡WH₃ and HE═WH₂ molecules for E = P and As. The potential energy surfaces for hydrogen transfer from PH₃ to the W were calculated at the coupled-cluster CCSD(T)/complete basis set level. Additional weak bands in the phosphide and arsenide W-H stretching region are assigned to the molecules with loss of H from W, E≡WH₂. The electronic structure calculations show that the E≡WH₃ molecules have a W-E triple bond, the HE═WH₂ molecules have a W-E double bond, and the H₂E-WH molecules have a W-E single bond. The formation of multiple E-W bonds leads to increasing stability for the isomers.