Abstract: Acombined experimental and theoretical studies of resonant ionization spectra for van der Waals complexes C₆H₅CH_3...Ar and C₆D₅CD_3...Ar are reported.By using resonant ionization spectrometry, together with time-of-flight mass spectrometry, in supersonic molecular beam, the internal rotation for CH₃and intermolecular vibration for atom Ar in the complexes are exhibited, all observed bands are rationally assigned by isotope effect and calculated at the internal rotational levels and external vibrational levels, and three modes frequencies of van der waals vibrations for complex C₆H₅CH_3...Ar are obtained.

Key words: Resonant photo-ionization spectra, Internal rotational spectra, van der Waals vibration