The sequential bond energies for complexes of Mg + with CO, CO 2 , NH 3 , CH 4 , CH 3 OH, and C 6 H 6 are determined by collision-induced dissociation (CID) with xenon or argon in a guided ion beam tandem mass spectrometer. The kinetic energy dependence of the CID and ligand exchange cross sections are analyzed to yield 0 and 298 K bond energies for Mg + -L after accounting for the effects of multiple ion-molecule collisions, internal energy of the reactant ions, and dissociation lifetimes. Bond energies (in eV) to Mg + at 0 K are determined for L ) Ar (0.10 ( 0.07), Xe (0.32 ( 0.12), 1-2 CO (0.43 ( 0.06 and 0.40 ( 0.03), 1-3 CO 2 (0.60 ( 0.06, 0.50 ( 0.03, and 0.46 ( 0.06), 1-5 NH 3 (1.60 ( 0.12, 1.27 ( 0.07, 0.99 ( 0.09, 0.45 ( 0.11, and 0.58 ( 0.12), 1-2 CH 4 (0.29 ( 0.07 and 0.15 ( 0.07), 1-3 CH 3 OH (1.51 ( 0.07, 1.25 ( 0.07, and 0.95 ( 0.09), and one C 6 H 6 (1.39 ( 0.10 eV). As expected for largely electrostatic interactions, the sequential bond energies generally decrease monotonically with increasing number of ligands. These values are in good agreement with theoretical values in the literature and ab initio calculations performed here, but the agreement is mixed for comparison with results of photodissociation measurements. Qualitatively, geometries of these complexes are controlled by interactions of the ligands with the single polarized valence electron on Mg + .

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.

The reactions of V+ (5D) with CS2 and COS and the reactions of VS+ with Xe, CO, COS, CO2, and D2 are studied as a function of translational energy in a guided-ion-beam (GIB) mass spectrometer. From these experiments, D 0(V+−S) = 3.78 ± 0.10 eV, D 0(V+−CS) = 1.70 ± 0.08 eV, and D 0(V+−SD) = 2.57 ± 0.15 eV are derived. Verification of D 0(V+−S) is achieved by probing reactions of V+ and VS+ in a Fourier transform ion cyclotron resonance mass spectrometer. The good agreement between the thermochemistry obtained in the V+/CS2 system and that from the other systems studied shows that the formally spin-forbidden formation of ground-state VS+ (3Σ-) from V+ (5D) and CS2 has no activation barrier in excess of the reaction endothermicity. At higher energies, the spin-allowed formation of VS+ (5Π) competes efficiently, giving rise to a composite shape of the VS+ cross section. The adiabatic and vertical splittings between the 3Σ- and 5Π states of VS+ are calculated as 1.37 and 1.87 eV at the MR-ACPF level of theory. These values agree well with the splittings obtained in GIB and sector-field mass spectrometric experiments.

Structural and thermochemical aspects of the FeS(2)(+) cation are examined by different mass spectrometric methods and ab initio calculations using density functional theory. Accurate threshold measurements provide thermochemical data for FeS(+), FeS(2)(+), and FeCS(+), i.e., D(0)(Fe(+)-S) = 3.06 +/- 0.06 eV, D(0)(SFe(+)-S) = 3.59 +/- 0.12 eV, D(0)(Fe(+)-S(2)) = 2.31 +/- 0.12 eV, and D(0)(Fe(+)-CS) = 2.40 +/- 0.12 eV. Fortunate circumstances allow a refinement of the data for FeS(+) by means of ion/molecule equilibria, and the resulting D(0)(Fe(+)-S) = 3.08 +/- 0.04 eV is among the most precisely known binding energies of transition-metal compounds. The present results agree with previous experimental findings and also corroborate the computed data for FeS(+) and FeS(2)(+). Ab initio calculations predict a sextet ground state ((6)A(1)) for FeS(2)(+) with a cyclic structure. The presence of S-S and Fe-S bonds accounts for the fact that not only reactions involving the disulfur unit but also sulfur-atom transfer can occur. In contrast, the FeS(2)(-) anion is an acyclic iron disulfide. In the gas phase, neutral FeS(2) may adopt either acyclic or cyclic structures, which are rather close in energy according to the calculations.

2000thermodynamic functions, thermochemistry thermodynamic functions, thermochemistry E 3000 -010Thermochemistry and Reactivity of Cationic Scandium and Titanium Sulfide in the Gas Phase.-The reactions of atomic Sc + and Ti + with COS and CS 2 and the reactions of ScS + and TiS + ions with Xe, CO, CO 2 , COS, H 2 O, and H 2 S in the gas phase are studied by guided-ion beam and Fourier transform ion cyclotron resonance mass spectroscopy. Bond dissociation energies for ScS + and TiS + , the equilibrium constants, reaction rate constants, and reaction enthalpies for the reactions of ScS + and TiS + with H 2 O are derived. Furthermore, the bond dissociation energies of Sc + -CS and Ti + -CS and the heat of formation of TiOS + are given. In addition to the experimental results density functional theory calculations of the electronic states and bond lengths of ScS + and TiS + are reported.