The dynamics of the reactions F+IX→IF+X (X=Cl, Br, I): A laser-induced fluorescence study

Abstract

The internal product state distributions of IF formed in the homologous exoergic reactions F+IX→IF+X (X=Cl, Br, I) were measured by the laser-induced fluorescence technique. The study was carried out with crossed molecular beams at collision energies of ∼3.2 kJ mol−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 (〈f′V〉=0.37, 0.27) and very low for X=I (〈f′V〉=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 〈f′R〉=0.16. The amount of translational excitation 〈f′T〉=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 the 2P1/2 state 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 the 2P1/2 state. The branching ratio k1/k2 for the two channels was determined to be k1/k2=0.90, 1.44, 0.12 for X=Cl, Br, I, respectively.