<p> In an investigation on the formation of halogen cations, the I4 2+, Br3+, Br2+ and Cℓ3+ cations have been identified by conductivity, cryoscopy, ultraviolet and visible spectrophotometry, Raman spectroscopy and magnetic susceptibility measurements in strong acids. Bromine trifluorosulphate has been shown to ionise in the SbF5:3SO3/HSO3F system to give the Br(SO3F)2+ ion, and Raman bands of bromine fluorosulphates, CℓSO3F and S2O6F2 have been listed. No evidence has been found for the Cℓ2+ or CℓF+ ions in solution, and the assignment of observed ESR spectra to these cations is criticised.</p> <p> Raman spectra of the adducts AsF5 2CℓF and BF3 2CℓF have shown that they contain the CℓCℓF+ cation and not the CℓFCℓ+ cation. The bending frequency of the CℓF2+ cation has been reassigned, and force constants have been calculated for the CℓF2+ and Cℓ3+ cations.</p> <p> Resonance Raman spectra of the I2+ and Br2+ cations have been observed, and, as few examples of this effect are known, the variation in fundamental and overtone intensities with exciting wavelength have been investigated.</p> / Thesis / Doctor of Philosophy (PhD)