The Theory of Long and Short Range Interactions for Solvated Electrons

Kennedy, Nairn Farquharson (1978) The Theory of Long and Short Range Interactions for Solvated Electrons. PhD thesis, University of Glasgow.

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On the basis of a review of experimental data on electron trapping in crystalline ice and liquid water, it may be conjectured that these media trap electrons at defect sites, which may be present in some quantity naturally, and can be augmented by additives or radiative disruption. This work reports the results of theoretical investigations into structures and situations possibly favourable to electron capture. Calculations are performed, using a flexible analytical wavefunction, on an electron trapped in a cavity in a linear, isotropic and homogenous dielectric in order to assess the contributions of long-range effects to electron trapping. Attention is then focussed on the short-range effects due to the detailed nature of the trapping site. After a discussion on possible criteria for trapping, two possible structures of a water dimer are examined, using a minimal basis set in ab initio UHF SCF MC calculations. The behaviour of energies, spin densities and excitation energies as intermolecular distance varies is discussed and the relevance of each structure to electron solvation is considered. This is succeeded by UHF INDO calculations on a water tetramer trapping site, using additional diffuse orbitals, and similar investigations on an (H2O)12 cluster. Other solvents are not neglected; the breathing modes of a methanol tetramer with up to eight molecules in two solvation shells are examined, and the behaviour of such structures with an excess electron considered. A larger basis set ab initio UHF calculation on an ammonia dimer illustrates the importance of hyperdiffuse orbitals in such treatments, and concludes that such a dimer in isolation will not stabilise a trapped electron. Since non-regular geometries may be relevant, especially in the initial capture of an electron, the umbrella vibration of NH3 is studied by ab initio UHF methods, with and without hyperdiffuse orbitals; in the excess electron state, the effect of these latter is marked, but no evidence of stabilisation with respect to the neutral state is apparent. Examination and discussion of all these resu3. ts leads to several conclusions: (i) because of the essentially arbitrary nature of its parameterization, the INDO method cannot yield definitive results on electron solvation. (ii) some structures can be labelled as possible electron traps, and others can be considered unlikely. This is detailed in the text. (iii) in all the structures studied, absolute energetic stabilisation with respect to the neutral state was not achieved; it is concluded that the long-range effects of the medium are an essential factor in stabilisation and must be included in the SCF calculations. The work concludes with an examination of the theoretical basis for molecular calculations which involve a surrounding dielectric medium, and identifies three main levels of approximation. The most sweeping of these is put forward as a useful guide to the magnitude of stabilisation energies, and suggestions for future work are made.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Physical chemistry
Date of Award: 1978
Depositing User: Enlighten Team
Unique ID: glathesis:1978-78782
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 30 Jan 2020 14:55
Last Modified: 30 Jan 2020 14:55

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