Guided ion beam studies of the state-specific reactions of Cr+ and Mn+ with CS2 and COS

Abstract

Reactions of Cr+ and Mn+ with CS2 and COS are studied using guided ion beam mass spectrometry. The electronic-state distributions of the metal-ion beams are systematically varied to probe the contributions of individual reactant states to the observed overall reactivity. The cross section for MnS+ formation in the reaction of Mn+ + COS exhibits two endothermic features corresponding to spin-forbidden formation of ground-state MnS+(5Π) and spin-allowed formation of excited-state MnS+(7Π). The cross section for MnS+ formation in the reaction of Mn++ CS2, and the cross sections for CrS+ formation in the reactions of Cr++ CSX (X = O, S) also appear to be composites, although the state-specific product cross sections are not resolved in these three systems. Cross sections for forming CrCS+ and MnCS+ in the CS2 systems and CrCO+ in the Cr++ COS reaction also exhibit two endothermic features, which are assigned to the formation of different structural isomers. From the thresholds associated with forming CrS+, CrCS+, MnS+, and MnCS+, we determine D0(Cr+ -S) = 2.68 ± 0.17, D0(Cr+-CS) = 1.69 ± 0.06, D0(Mn+-S) = 2.52 ± 0.24, and D0(Mn+-CS) = 0.83 ± 0.22 eV. Results of the Cr++ CS2 reaction suggest that the initial step in the activation of CS2 by Cr+ is insertion of the metal ion into one of the C–S bonds.