ROTATIONAL RAMAN SPECTROSCOPY OF ETHYLENE USING A FEMTOSECOND TIME-RESOLVED PUMP-PROBE TECHNIQUE

Abstract

Femtosecond Raman-induced polarization spectroscopy (RIPS) has been conducted at low pressure (170 and 300 mb) in ethylene. The temporal signal, resulting from the beating between pure rotational coherences, was measured with an heterodyne detection at two different temperatures (293 and 373 K). The temporal traces were converted to the frequency domain using a Fourrier transformation and then analyzed thanks to the $D_{2h}$TDS software}$^,$}, in press (2005).} dedicated to X$_2$Y$_4$ molecules with $D_{2h}$ symmetry. The effective Hamiltonian was expanded up to order two, allowing the determination of five parameters with a RMS of 0.017 cm$^{-1}$. Special care was put on the precise modeling of intensities, taking into account all instrumental effects (pulse durations, {\em etc}). Relative intensities were fitted and two polarizability operators were determined.