Towards a complete description of multiple dissociation events:: A photoion-photoneutral (pi-pn3) coincidence study Ar4+

By combining the techniques of ion and fast neutral detection into a single coincidence experiment, it is demonstrated that the scattering patterns of all the fragments from a multiple dissociation event can be correlated. The power of this new technique is demonstrated using Ar-4(+) as an example, where photoexcitation generates a total of 7 possible reaction products, each of which is, in theory, distinguishable by charge and/or kinetic energy. The two ionic products are Ar+ and Ar-2(+), and whilst the latter ion emerges with a low kinetic energy and is isotropically scattered, Arf has associated with it both a significant spread in laboratory-frame kinetic energy and features indicative of anisotropic scattering. By selecting an appropriate laboratory-frame kinetic energy for either ion, coincident neutrals can be identified and energy-analyzed using a time-of-flight technique. The methods reveals the presence of two separate fragmentation channels, one of which is concerted and the other sequential. (C) 1998 American Institute of Physics.