On the Collision Mechanism of Bimolecular Reactions. Part I. Theory and Experimental Method for the Determination of the Velocity Spectrum of Products from Simple H-Transfer Reactions of the Type X(+) +H2 to XH(+) +H,

A simple apparatus is described which allows one to measure the velocity spectrum of the XH or XD ions, respectively, resulting from ion-molecule reactions of the type X H2D2 forming XH HXD D. The secondary ions are not accelerated after their formation. The incident X-ions have kinetic energies between 20 and 200 cV. Furthermore, the velocity spectra are calculated which have to be expected for different collision models. 1 Complex model All the atoms in the reactants participate in the collision. Every kind of collision between those limiting cases is conceivable, in which the relative kinetic energy of the reactants and the heat of reaction appear as internal energy of the product ion or as kinetic energy of both products completely inelastic and elastic collision with atomic rearrangement, respectively. 2 Stripping model The incident X-particle hits only one atom of the hydrogen molecule in a completely inelastic collision without transfer of momentum to the second hydrogen atom. It is also shown that the cross section of the reaction becomes zero above a certain energy of the incident ion. This critical energy depends on the collision mechanism. It can be measured with the apparatus described. In addition an isotope effect of the order of 2 with respect to the critical energy is expected from the transfer of an H or D atom, respectively.