Observed differential reaction cross section of the CH3I+Na→NaI+CH3system

Using the crossed molecular beam method complete laboratory differential reaction cross sections for the exoergic reaction CH3I+Na→NaI+CH3 have been measured as a function of relative translational energy E T from 0·13 to 0·42 eV and an analysis was made of these NaI laboratory angular distributions over the range of reactive translational energy. By using the uncoupled approximation for the centre of mass angular and recoil energy to recover the laboratory angular distributions it was found that the centre of mass differential (solid angle) reaction cross sections to be backward-peaked, characteristic of a direct, rebound mechanism, with a large fraction of the available energy going into product translation. The average translational energy of the products ′T increases approximately linearly with increasing collision energy, ′T/kJ mol-1=0·73 ( T/kJ mol-1)+50·6. An analysis of these differential cross section, as well as for the related K and Rb reactions, was carried out by using the direct interaction with product repulsion-distributed as in photodissociation (DIPR-DIP) model, from which it was concluded that it can account satisfactorily for the main features of the observed cross section. A discussion in terms of an electron jump mechanism prior to the product repulsion, including an attack angle dependence in the reaction dynamics, that is, a steric factor functionality, is also presented.