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Raman‐induced polarization spectroscopy (RIPS) experiments were conducted at room temperature and pressures below 2 atm in pure N2 and CO2. Both homodyne and optically heterodyne detection were used. Calculations of the signal as a function of the pump–probe delay were performed taking into account the pulse duration of the laser, the rotational dependence of the dephasing rates and the small instantaneous electronic Kerr effect. The observed decay and shape of the rotational quantum beats are in good agreement with the calculations. Several sets of linewidth coefficients corresponding to the diagonal part of the collisional–rotational relaxation matrix were used. This matrix was choosen among available models derived from wavenumber domain studies (fitting and scaling laws). The energy‐corrected sudden model derived from extensive wavenumber domain studies reproduces the experimental data well. A comparison between different models is discussed. Copyright © 2000 John Wiley & Sons, Ltd.

In this paper we present a tensor analysis of Raman induced polarization spectroscopy (RIPS), a variation of time-resolved rotational coherence spectroscopy (RCS), developed in our laboratory to study coherent rotational motions in fluids over a range of densities. Based on the irreducible tensor algebra, the analysis separates the fundamental molecular response in RIPS from the dependence of the signal on geometric factors (i.e., laser polarizations). Explicit formulas for the femtosecond RIPS response of symmetric and asymmetric tops are derived. The results are in good agreement with experimental RIPS spectra of low pressure CO2 and O3. The tensor analysis is also generalized to other types of four wave mixing experiments, allowing detailed comparison of the various frequency- and time-domain pump–probe experiments.

We report a new variant of the femtosecond transition-state spectroscopy technique−transient stimulated emission pumping (TSEP). The initial application of TSEP to studies of ozone visible photodissociation indicates that the molecule is trapped in the Franck–Condon region for ∼90 fs. The wave packet then spreads along the reaction coordinate.

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