Using the recently developed method of coherent ion dip spectroscopy (CIS), we were able to measure rotationally resolved spectra of high lying overtones of the intermolecular van der Waals vibrations of the benzene-Ar complex. Optimized pulse sequences for the CIS experiment were obtained by numerical calculations of the population dynamics in the coherently excited few-level system. Due to the high resolution achieved in this experiment, the small isotope shifts upon deuteration of the benzene molecule could be measured and compared with the simple classical harmonic oscillator and with anharmonic three-dimensional quantum calculations. By comparing the latter calculations with the results of the CIS experiments, we tested the quality of several benzene-Ar interaction potentials.