The CH3+Arn complexes are investigated for n up to 8. The molecular structures, dissociation energies, and vibrational frequencies of those complexes are studied, and the nature of the interactions is discussed. All possible structural isomers were considered. The formation of clusters is based on the consecutive filling of four distinct shells. The theoretically determined consecutive dissociation energies are in excellent agreement with experimental data derived from infrared photodissociation spectra and pulsed electron beam high-pressure mass spectrometry. The influence of an argon environment on the electron affinity of the CH3+ ion is also discussed.