Reactions of $Pt+$ with $H2,$ $D2,$ and HD: Effect of lanthanide contraction on reactivity and thermochemistry

A guided ion beam tandem mass spectrometer is used to examine the kinetic energy dependence of reactions of the third-row transition metal cation, $Pt+,$ with molecular hydrogen and its isotopologs. A flow tube ion source produces $Pt+$ ions in its electronic ground state term and primarily in the lowest spin–orbit level. Corresponding state-specific reaction cross sections are obtained. Modeling of the endothermic reaction cross sections yields the 0 K bond dissociation energy of $D0(Pt+–H)=2.81±0.05 eV$ $(271±5 kJ/mol).$ The experimental thermochemistry is consistent with ab initio calculations, performed here and in the literature. Theory also provides the electronic structures of these species and is used to examine the reactive potential energy surfaces. Results from reactions with HD provide insight into the reaction mechanisms and indicate that the late metal ion, $Pt+,$ reacts largely via a direct mechanism. Results for this third-row transition metal system are compared with the first-row and second-row congeners and found to have higher reactivity towards dihydrogen and stronger $M+–H$ bonds. These differences can be attributed to lanthanide contraction and relativistic effects.