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We report studies of the rotationally resolved $S1-S0$ electronic spectra of aniline and its van der Waals complex with a single Ar atom. Analysis of these spectra leads to a determination of the vibrationally averaged structures of the bare molecule and the complex in the two electronic states. Aniline itself is pyramidally distorted at the $NH2$ group in the $S0$ state. Attachment of the Ar atom on the side of the ring opposite to the two NH bonds converts the symmetric double well along the inversion coordinate to an asymmetric one, in the ground state. The excited state is quasi-planar along this coordinate. At higher vibrational energies in the $S1$ state, we also observe in the spectra of the complex line broadenings and spectral peturbations, a consequence of vibrational predissociation (VP) The important role of intraintermolecular mode mixing (i.e., IVR) in promoting the VP process is elucidated from these data.