DETERMINATION OF REACTION GEOMETRIES

Using polarized light the reaction geometry of selected species can be controlled even in bulk experiments. One reactant A is generated in a photodissociation process and its spatial distribution is completely described by the anisotropy parameter beta. The other molecular reacta nt B is excited in a specific rovibrational state. Its spatial distrib ution is given by the J- and branch-dependent alignment parameter A(0) ((2)). Equations have been developed that allow a relatively easy conv ersion of experimental results to the angle of attack, gamma. The unno rmalized probability of an attack of A on B under an angle gamma is gi ven by the simple expression P(gamma)proportional to[1 + 1/5 beta A(0) ((2))(cos gamma)P-2(cos delta)] where delta is the angle between the ( E) over right arrow vectors of the dissociating and the exciting laser beam. As an example, we have studied the reaction of A+HCN-->HA+CN wi th A = H,Cl. The experimental results prove a preferred linear reactio n geometry, i.e, an end-on attack of atom A on the terminating hydroge n atom of the HCN reactant. However, the cone of acceptance is higher for the Cl + HCN reaction than for the H+HCN one. (C) 1997 American In stitute of Physics.