1. Cation radical cycloadditions and related sigmatropic reactions
2. Pericyclic reactions of radical cations
3. An ab initio theoretical reaction path study of the cation radical Diels-Alder reaction
4. External generation of ions in ICR spectrometry
5. Molecular orbital calculations have been done using the GAUSSIAN86 series of program (Gaussian Inc., Pittsburg, PA, USA (1990)). Total geometry optimizations were conducted with the 3-21G basis set of atomic orbitals without symmetry constraint (geometrical parameters are available upon request from the authors). In view of the size of the system, the investigation has been limited to this level of theory. However, examination of Table 3 reveals good agreement between calculation and experiment.