Thermochemistry for the Gas-Phase Ion-Molecule Clustering of CO2+CO2, SO2+CO2, N2O+N2O, O2+CO2, NO+CO2, O2+N2O, and NO+N2O: Description of a New Hybrid Drift Tube/Ion Scoure with Coaxial Electron Beam and Ion Exit Apertures

Article abstract of DOI:10.1021/j100321a037

A mass spectrometer ion scoure designed specifically to measure high-pressure gas phase ion-molecule equilibria as a function of temperature was developed.The ion source has coaxial electron entrance and ion exit apertures.Ions move through the source at a constant velocity determined by a uniform electric field gradient which is controlled by overlapping drift guard rings.The transport properties of Ar⁺ (mobility and diffusion) demonstrate that the effect of the electric field is negligible compared to thermal energies.Equilibria were investigated for the reactions forming the following gas-phase ion-molecule clusters: CO2⁺CO2, SO2⁺CO2, N2O⁺N2O, O2⁺CO2, NO⁺CO2, O2⁺N2O, and NO⁺N2O.The measured enthalpies and entropies of reaction were used to determine the cluster ion enthalpies and entropies of formation at 298 K.The bond energies (from the enthalpies at 0 K) were determined to be for CO2⁺CO2, D₀ deg = 15.9 kcal/mol; for SO2⁺CO2, D₀ deg = 10.2 kcal/mol; for N2O⁺N2O, D₀ deg 13.3 kcal/mol; for O2⁺CO2, D₀ deg = 9.8 kcal/mol; for NO⁺CO2, D₀ deg = 8.6 kcal/mol; for O2⁺N2O, D₀ deg = 10.8 kcal/mol; and for NO⁺N2O, D₀ deg = 7.7 kcal/mol.The experimental entropies of reaction for the formation of O2⁺N2O and NO⁺N2O are substantially less negative than those for O2⁺CO2 and NO⁺CO2.The entropy differences are large enough to suggest an inherent difference between the bonding or geometry for the ions bound to N2O compared to those bound to CO2