Determination of rotational constants in a molecule by femtosecond four-wave mixing

Femtosecond time-resolved DFWM experiments were performed on CHCl3 and SO2, The recurrences observed originate from the preparation of rotational cohe rences within the sample. The determination of rotational constants for a s ymmetric and an asymmetric top are shown. The simulation of the transients for the symmetric top allows the extraction of the main moment of inertia B and the centrifugal terms perpendicular to the molecule axis. For the asym metric top, all three rotational constants can be derived. In addition to t he transients at 1/2(B + C), two additional types of asymmetry transients a t 1/4C and 1/4A arise from this experiment. The first origins from the leve ls at low K and the second from the levels at high K in the high-J limit. C opyright (C) 2000 John Wiley & Sons, Ltd.