The internal product state distributions of IF formed in the homologous exoergic reactions F+IXrarr;IF+X (X=Cl, Br, I) were measured by the laserhyphen;induced fluorescence technique. The study was carried out with crossed molecular beams at collision energies of sim;3.2 kJthinsp;molminus;1. The observed bimodal IF vibrational product state distributions indicate microscopic branching. The average fraction of the total energy available channeled into vibration is modest in the case of X=Br, Cl (lang;fprime;Vrang;=0.37, 0.27) and very low for X=I (lang;fprime;Vrang;=0.07). For the reaction F+ICl, rotational population analysis could be carried out. The average fraction of rotational product excitation was found to be lang;fprime;Rrang;=0.16. The amount of translational excitation lang;fprime;Trang;=0.15 was determined by Wong and Lee for the reaction F+I2. Since this value is also low, a substantial amount of the exoergicity must be channeled into electronic excitation of the2P1/2state of the product halogen atoms. The bimodal vibrational product state distributions are interpreted as resulting from two microscopic pathways: (1) a direct channel leading to the formation of highly vibrationally excited IF and (2) a complex interaction which results in monotonically decreasing IF distributions at low vibrational levels and halogen product atoms in the2P1/2state. The branching ratiok1/k2for the two channels was determined to bek1/k2=0.90, 1.44, 0.12 for X=Cl, Br, I, respectively.
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