Methods of generation and characterization of radical cations in low t
emperature matrices are briefly presented. Advantages of steady-state
and pulse radiolysis in the application to studies of low barrier isom
erization processes in radical cations are described. Unimolecular rad
ical cation transformations such as valence isomerization, conformatio
nal rotamerism and enolization studied by low temperature pulse radiol
ysis are reviewed.