Determining gas phase properties by ion-molecule reactions

The reactions between ions and molecules were monitored to probe physical properties of gas-phase molecules: ionization energies and double bond positions. The ionization energies of a series of n-alkanes C8 to C22 were determined by temperature dependent equilibrium studies in which the initial rates for charge transfer reactions between n-alkanes and fluorinated benzenes with known ionization energies were measured. The values for DeltaH° and DeltaS° of charge transfer were measured. Significant DeltaS° values were observed and there was a trend of increasingly negative values with increasing carbon number. A trend of decreasing ionization energy was observed with increasing carbon number. Up to C22, the ionization energies of n-alkanes do not reach a constant value.; The Gaussian 98 computational package was used to calculate the energy differences between molecules and molecular ions, and from these energy differences, vertical and adiabatic ionization energies were calculated. Two ab initio theories (Hartree Fock and MP2) and one density functional theory (B3LYP) were used to calculate the ionization energies of n-alkanes C2 to C7. The molecular ions had predicted geometries that varied for each theoretical method. The ionization energies of n-alkanes showed no consistent trend for the ab initio methods. There was a decrease in ionization energy from B3LYP calculations with increasing carbon number; however, the ionization energy values were different from the accepted literature values. The ionization energies of a series of C6 compounds with different functional groups and a series of n-alkyl amines were calculated by B3LYP and shown to be different from the accepted literature values, although a trend for decreasing ionization energy with increasing carbon number was observed.; The reactions of olefin molecular ions with olefin molecules were observed in both FT/ICR and ion trap instruments. The reactions of olefin molecular ions C7 to C10 with cyclohexene were investigated and shown to produce even mass product ions which could be used to identify double bond position.; FT/MS was used to monitor the reactions of olefin molecular ions with their parent neutrals. (Abstract shortened by UMI.)...