The F+ I2 4 IF+ I reaction has been studied in a crossed-beam experiment. The IF rovibrational distribution has been measured with the laser-induced fluorescence detection technique. Many new and important results concerning the energy disposal in this reaction are thus obtained. Moreover, a bimodal rotational distribution is observed in several vibrational levels: this phenomenon seems to be due to migratory collisions.

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We have measured the differential cross section of the F+I2→IF+I reactive collision as a function of the rovibrational state of IF. This measurement was made by an analysis of the Doppler profiles of the laser-induced fluorescence detection signals, as suggested by Kinsey [J. Chem. Phys. 66, 2560 (1977)]. This paper describes in detail the experiment and the way we analyze the data to deduce the differential cross section. The shape of the cross section appears to vary noticeably with the rotational energy of IF and to a lesser extent with its vibrational energy. Several partial explanations are possible, and the choice remains not clear as long as we have no precise information on the potential-energy surfaces of the I2F system.

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We have performed a crossed beam study of the F+I2→IF+I reaction. The IF product was detected by the LIF technique, using a cw single frequency dye laser. About 10 000 lines belonging to the B–X system of IF have been thus recorded. These lines have been assigned and the populations of about 1300 rovibrational levels of the X state were deduced from their intensities. This analysis takes into account the coherent saturation regime of the excitation process. In the present work, only the high vibrational levels of the X state (v″=8–20) have been studied. A striking result is the observation of bimodal rotational distributions for several vibrational levels: the rotational distribution presents a plateau and a peak for high rotational quantum numbers. The vibrational distribution presents a peak centered at v″=13, and as we have shown that the v″=0 peak observed by other authors is in fact an experimental artifact, the general features of the energy disposal in this reaction are now well known.