Femtosecond degenerate four‐wave mixing study of benzene in the gas phase

We report on time‐resolved rotational spectroscopy of benzene molecules both in a gas cell at room temperature (298 K) and in a supersonic expansion (30 K) by femtosecond degenerate four‐wave mixing (fs‐DFWM). A detailed study of the time‐dependent structure of the rotational recurrences for the gas cell is presented. Moreover, for the first time, the fs‐DFWM technique has been applied to a medium‐sized molecule in the collision‐free environment of a seeded supersonic expansion up to a time delay of 4 ns. From these data, by fitting of the experimental spectra, a rotational constant B = 5688.95 ± 0.55 MHz was obtained for benzene in the gas cell and B = 5689.25 ± 0.11 MHz for benzene in the supersonic expansion. The combination of gas cell and supersonic jet investigations by fs‐DWFM provides a means for the structural study of large and more complex molecules. Copyright © 2002 John Wiley & Sons, Ltd.