Optically detected ESR and magnetic field effect on recombination luminescence yield (MARY) spectroscopy of spin-correlated radical ion pairs were used to study cis- and trans-decalin radical cations in nonpolar solutions. The differences observed in cis- and trans-decalin spectra are demonstrated to agree with the existence of temperature-activated intramolecular dynamic transitions in trans-decalin radical cation. In diluted solutions with decalin added as accepters, the MARY spectroscopy technique yields the spectra of the corresponding radical cations even at room temperature. Under these conditions, the fast limit of dynamic transitions in trans-decalin radical cation takes place. It is demonstrated that both cis- and trans-decalin radical cations take part in ion-molecular charge transfer to a neutral molecule, the rate constant being close to the diffusion-controlled one.