This thesis can be divided into two parts.The aim of the studies described in the first part of the thesis isto make clear the dominating processes in the selective decorrpositionof certain solutes that follow low-terrperature radiolysis of crystalline hydrocarbons. 1. The isotope effect in the production of radicals has been studiedby Electron Spin Resonance and Gas Chromatography/MassSpectrometry in the C10H22/C10D22 system. Two independent methodshave never been used on the same system in this contextbefore. The methods gave the same ratio of protiated to deuteratedradicals. 2. The isotope effect in the production of hydrogen gas has beenstudied with Mass Spectrometry in the C10H22/C10D22 system. 3. The amount of reactive D-atoms has been measured in C10D22 using an olefin, C10H20, as a scavanger. 4. The effect of an electron scavenger, C8H16Cl2, in C10H22 has been investigated. Two processes for the explanation of the isotope effects are discussed. a. transfer of excitation energy b. selective abstraction. The results show that reactive D-atoms are present in the C10D22 system and suggest that the isotope effects can be explained by selectiveabstraction. The effect of the electron scavenger can beexplained by energy transfer, but not entirely by selective abstraction. In the second part of the thesis, a method to simulate Electron SpinResonance spectra for the case of a Hamiltonian containing nuclearinteractions is described. The method has been applied to the S = 1 case. It is suggested that the method can be generalized to an arbitraryelectronic spin state, and to include second order nuclear corrections. / digitalisering@umu