A study of matrix isolated ions by electron spin resonance spectroscopy
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
The objective of this project was to attempt to trap small molecular ions in an argon matrix and study the structure of these ions using electron spin resonance spectroscopy. To this end an apparatus designed for matrix isolation ESR was developed in a number of stages concurrently with matrix isolation experiments. Early experiments used conventional electron impact ion sources but these sources were found to be unsuitable for producing ions to trap in an argon matrix due to the energy of the ions. In these experiments problems arose due to contamination of the matrix by methyl radicals and hydrogen and nitrogen atoms which obscured the spectral range of interest that is around g = 2. Vacuum ultra-violet photolysis was used to produce ions and was found to be successful. The molecular ion NH₃⁺ has been trapped in an argon matrix at 14K by photo-ionisation of an NH₃/Ar mixture during deposition. The NH₃⁺ cation has been found to be rigidly trapped in the argon matrix and exhibits a powder-type ESR spectrum. The derived magnetic parameters agree well with those obtained by other workers in different matrices. A strong reversible temperature dependence of the linewidth of the NH₃⁺ spectrum has been observed. Argon resonance photolysis of methyl iodide and methyl bromide argon mixtures during deposition was found to produce free methyl radicals in addition to methyl radicals interacting weakly with a high spin nucleus or nuclei. These species have been tentatively assigned on chemical evidence as CH3̇ ⋯ and CH3̇ ⋯ Br- respectively. The complexity of the spectra resulted in complete solution not being possible.