Molecular Beam Kinetics: Reactions of K and Cs with Alkyl Dihalides

Crossed beam studies have been made of the reactions of K and Cs atoms with CH2I2, CH2Br2, CH3CHBr2, (CH3)2CBr2, and CH2Cl2. The CH2I2 reactions show properties similar to reactions of diatomic alkali molecules: the reaction cross sections are very large (≳150 Å2); the angular distribution of the alkali halide product peaks forward (in the center-of-mass system) with respect to the incident alkali beam; and the most probable translational energy of the products is a small fraction (≲10%) of the available energy (∼ 35 kcal/mole). The RBr2 systems show more distinctive behavior: the reaction cross sections are two or three times larger for Cs than for K (∼ 50 Å2) but do not vary much with size of the alkyl group; the product angular distributions peak sideways, favoring the forward hemisphere for Cs, the backward hemisphere for K; and the product translational energy is a major fraction (roughly estimated as ∼ 50%) of the available energy (∼ 30 kcal/mole) for both the Cs and K reaction. For CH2Cl2 the reaction cross sections are below the detection limit (≲5 Å2). The variations in dynamical properties among these and other reactions are discussed in terms of the electron-jump model.