Guided ion beam and theoretical studies of the reaction of Ru+ with CS2 in the gas-phase: thermochemistry of RuC+, RuS+, and RuCS+

Abstract

The gas-phase reactivity of the atomic transition metal cation, Ru⁺, with CS₂ is investigated using guided-ion beam mass spectrometry (GIBMS). Endothermic reactions forming RuC⁺, RuS⁺, and RuCS⁺ are observed. Analysis of the kinetic energy dependence of the cross sections for formation of these three products yields the 0 K bond energies of D₀(Ru⁺–C) = 6.27 ± 0.15 eV, D₀(Ru⁺–S) = 3.04 ± 0.10 eV, and D₀(Ru⁺–CS) = 2.59 ± 0.18 eV, and consideration of previous data leads to a recommended D₀(Ru⁺–C) bond energy of 6.17 ± 0.07 eV. A detailed reaction coordinate surface for these processes is determined by quantum chemical calculations and shows that all three reactions take place by insertion to form a S–Ru⁺–CS intermediate. Although multiple spin states are available, the reaction appears to occur primarily on the quartet ground state surface, although coupling to a sextet surface is required to form the RuS⁺(⁶Σ⁺) + CS(¹Σ⁺) ground state products. Calculations are used to locate the approximate crossing points between the quartet and sextet surfaces, finding them in both the bending coordinate of the S–Ru⁺–CS intermediate and in the exit channel. Elimination of S₂ to form RuC⁺ follows a much more complicated pathway involving a cyclic RuCSS⁺ intermediate, consistent with the energetic behavior of the experimental RuC⁺ cross section.