Activation of C–H bonds in the sequential reactions of Pt+ + x(CH4/CD4), where x = 1–4, have been investigated using infrared multiple photon dissociation (IRMPD) spectroscopy and theoretical calculations. Pt+ cations are formed by laser ablation and exposed to controlled amounts of CH4/CD4 leading to [Pt,xC,(4x-2)­H/D]+ dehydrogenation products. Irradiation of these products in the 400–2100 cm–1 range leads to CH4/CD4 loss from the x = 3 and 4 products, whereas PtCH2 +/PtCD2 + products do not decompose at all, and x = 2 products dissociate only when formed from a higher order product. The structures of these complexes were explored theoretically at several levels of theory with three different basis sets. Comparison of the experimental and theoretical results indicate that the species formed have a Pt­(CH3)2 +(CH4) x‑2/Pt­(CD3)2 +(CD4) x‑2 binding motif for x = 2–4. Thus, reaction of Pt+ with methane occurs by C–H bond activation to form PtCH2 +, which reacts with an additional methane molecule by C–H bond activation to form the platinum dimethyl cation. This proposed reaction mechanism is consistent with theoretical explorations of the potential energy surface for reactions of Pt+ with one and two methane molecules.

The sequential activation of up to 4 CH4 molecules by Ir + is investigated through a gasphase infrared multiple photon dissociation (IRMPD) experiment and theoretical calculations. A molecular beam apparatus was used to generate Ir + by laser ablation and expose it to controlled amounts of CH4. Product ions were irradiated with IR light from a free electron laser over the 500-1800 cm-1 spectral range and photodissociation was monitored using a time-of-flight mass spectrometer. Experimental spectra were obtained for five distinct species: [