Chad Rue

Kinetic-energy dependence of competitive spin-allowed and spin-forbidden reactions: V++CS2

The kinetic-energy dependence of the V++CS2 reaction is examined using guided ion-beam mass spectrometry. Several different ion sources are used to systematically vary the V+ electronic state distributions and elucidate the reactivities of both the ground and excited state V+ cation. The cross section for VS+ formation from ground state V+(5D) exhibits two endothermic features corresponding to the formation of ground state VS+(3Σ−) and excited state VS+(5Π). The thresholds for these two processes are in good agreement with theoretically determined excitation energies. The cross section for spin-forbidden formation of ground state VS+(3Σ−) exhibits an unusual variation with kinetic energy that is attributed to the energy dependence of the surface-crossing probability. From the thresholds associated with the formation of VS+ and V(CS)+, D0(V+–S)=3.72±0.09 eV and D0(V+–CS)=1.70±0.08 eV are derived. Further, circumstantial evidence for formation of a high-energy isomer of V(CS)+ is obtained.

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

Abstract Reactions of Cr + and Mn + with CS 2 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 + ( 5 Π) and spin-allowed formation of excited-state MnS + ( 7 Π). The cross section for MnS + formation in the reaction of Mn + + CS 2 , 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 CS 2 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 D 0 (Cr + S) = 2.68 ± 0.17, D 0 (Cr + CS) = 1.69 ± 0.06, D 0 (Mn + S) = 2.52 ± 0.24, and D 0 (Mn + CS) = 0.83 ± 0.22 eV. Results of the Cr + + CS 2 reaction suggest that the initial step in the activation of CS 2 by Cr + is insertion of the metal ion into one of the C–S bonds.

Reactions of Ta+ and W+ with H2, D2, and HD: Effect of lanthanide contraction and spin-orbit interactions 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 cations, Ta+, and W+, with molecular hydrogen and its isotopologs. A flow tube ion source produces Ta+ and W+ ions in their 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 energies in eV (kJ/mol) of D0(Ta+–H)=2.38±0.06 (230±6) and D0(W+–H)=2.27±0.05 (219±5). The experimental thermochemistry is consistent with ab initio calculations, performed here and from the literature, which also provide the electronic structures of these species and details about the reaction surfaces. Results from reactions with HD provide insight into the reaction mechanisms and indicate that these early metal ions, Ta+ and W+, react largely via insertion mechanisms. Results for these third-row transition metal systems a...