The Cs(7P)+H2→CsH+H reaction is studied in a crossed-beam experiment with laser-induced
fluorescence detection of CsH products. The usual flux (≈50mW/mm2) which is delivered by the C.W.
tunable dye laser used in the experiment is enough to saturate the absorption by CsH products. Then, by
crossing twice the laser beam through the collision volume (counterpropagating beams), one realizes the
conditions of saturated-absorption experiments: when the laser frequency is tuned to a resonance
frequency of CsH products, a defect to absorption occurs for these products which scatter in the collision
plane and a "saturation dip" appears at the center of the corresponding fluorescence profile. Application
of this technique to crossed-beam experiments can lead to the selection of product molecules which scatter
in any definite plane. A different geometry of the laser beams (bent beams) is proposed to select molecules
which scatter in any definite direction: it could be applied to detect an asymmetry in the scattering of the
products with respect to the collision axis, when a particular preparation of the reagents is realized.
