Theoretical studies of anisotropic ion transport systems (1993)
AuthorsGrice, Stephen T.show all
Ab initio calculations of potential energy surfaces have been applied to a range of chemical problems. Specifically these methods have been applied to the Diels-Alder reaction between butadiene and acetylene. The structure of the reactants, the Cs transition state, and the products have been calculated. The transition state geometry and energy is analysed in terms of orbital interactions and distortion energy relative to the separated reactants. The increase in energy of the filled π-orbital of acetylene not involved in bonding changes is the major contributor to the activation energy for the Diels-Alder reaction of butadiene with acetylene being greater than that found between butadiene and ethylene. Comparisons with a series of other related Diels-Alder reactions are discussed. The calculation of interaction potentials of a series of open shell ions with helium has been combined with moment method calculations to determine the ion transport properties of systems that involve anisotropy. First the theory of the moment methods used to calculate the transport properties of ions in dilute gases is reviewed. The theory for spherically symmetric ions in a spherically symmetric gas is briefly discussed, followed by a review of the recent specialisation of the theory for diatomic ions in diatomic gases to atomic ions in a diatomic gas. The theory of spherically symmetric systems is then applied to open shell ions that have orbital angular momenta greater than zero. Any theoretical treatment of the ion transport properties of such ions must recognise that more than one collision channel is available to the collision partners. Two classical models are developed that involve non-adiabatic transitions between these collision channels during a collision and between collisions. The models are used to study the mobilities of the following ions: C⁺ (² P), C+* (⁴P), N⁺(³ P), O⁺ (48), O⁺* (± P), Si⁺(²P), Si⁺* (⁴P). A summary and discussion is given. The theory of atomic ions in diatomic gases is then applied to the Li⁺ — N₂ and the Li⁺ — CO systems. Ab initio calculations of the rigid rotor potential energy surfaces for these systems are followed by calculations of the transport cross sections and transport coefficients. Comparisons of the transport coefficients derived from existing potential energy surfaces show that the potential energy surfaces calculated in this work are significantly better, and as good as can be derived from comparison of the theoretical and experimental ion transport results.