TOWARDS A COMPLETE DESCRIPTION OF MULTIPLE DISSOCIATION EVENTS - A PHOTOION-PHOTONEUTRAL (PI-PN(3)) COINCIDENCE STUDY AR-4(+)

By combining the techniques of ion and fast neutral detection into a s ingle coincidence experiment, it is demonstrated that the scattering p atterns 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 possi ble 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 i s isotropically scattered, Arf has associated with it both a significa nt spread in laboratory-frame kinetic energy and features indicative o f 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 reve als the presence of two separate fragmentation channels, one of which is concerted and the other sequential. (C) 1998 American Institute of Physics.