Coherent ion dip spectroscopy of the ground state benzene-Ar complex. Vibration-rotation levels up to 130 cm(-1) intermolecular energy

Coherent ion dip spectroscopy (CIS) provides high sensitivity and high resolution for the investigation of vibrational overtones in molecular electronic ground states. For a special time sequence of two coherent narrow-band Fourier transform limited nanosecond UV light pulses, with a modest delay of the pump pulse of 6.4 ns, a complete blocking of the population transfer to the upper state is achieved in the lambda-type three-level system ion dip experiment. This leads to ion dips with a depth as large as 95 per cent and each dip represents an individual rovibronic transition. In this work, CIS is applied for the first time to a weakly bound van der Waals complex, benzene-Ar. We are able to observe six new van der Waals vibrational states up to an excess energy of 130 cm(-1). The assignments are made by comparison with recent S1 excited state data of benzene-Ar and p-difluorobenzene-Ar and by analysis of the positions and intensities of the observed individual rotational lines. The fre quency positions of the intermolecular vibrational states display a regular pattern up to 130 cm(-1).