Influence of the transverse velocity on TC-RFWM spectra of jet-cooled CH

A saturation dip has been observed recently by A. Kumar et al. [Chem. Phys. Lett. 297 (1998) 300] in degenerate four-wave mixing (DFWM) and two-color resonant four-wave mixing (TC-RFWM) spectra of jet-cooled CH. This observat ion suggests that expressions of the signal intensity established for doubl e-resonance molecular spectroscopy in the weak held limit are no longer val id. While the line splitting has been explained, this is not the case for t he asymmetry observed on this spectrum. Here, we clearly establish the orig in of this asymmetry as resulting from the transverse molecular velocity wh ich acts even for a small velocity component. The model conveniently reprod uces line splitting and asymmetry. (C) 2001 Elsevier Science B.V. All right s reserved.