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

Abstract

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 (${\text{≳150 Å}}^2$ ); 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 ($\text{≲10\%}$ ) of the available energy ($\text{∼ 35}\mathrm{kcal}/\mathrm{mole}$ ). The RBr₂ systems show more distinctive behavior: the reaction cross sections are two or three times larger for Cs than for K (${\text{∼ 50 Å}}^2$ ) 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 $\text{∼ 50\%}$ ) of the available energy ($\text{∼ 30}\mathrm{kcal}/\mathrm{mole}$ ) for both the Cs and K reaction. For CH₂Cl₂ the reaction cross sections are below the detection limit (${\text{≲5 Å}}^2$ ). The variations in dynamical properties among these and other reactions are discussed in terms of the electron‐jump model.