Coherent ion dip spectroscopy of the ground state benzene–Ar complex: Vibration–rotation levels up to 130 cm−1 intermolecular energy

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Abstract
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% 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 S 1 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 frequency positions of the intermolecular vibrational states display a regular pattern up to 130 cm−1.

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