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 reactant B is excited in a specific rovibrational state. Its spatial distribution is given by the J- and branch-dependent alignment parameter A(0)((2)). Equations have been developed that allow a relatively easy conversion of experimental results to the angle of attack, gamma. The unnormalized probability of an attack of A on B under an angle gamma is given 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 with A = H,Cl. The experimental results prove a preferred linear reaction geometry, i.e, an end-on attack of atom A on the terminating hydrogen 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 Institute of Physics.