ON THE DISTINCTION BETWEEN TIGHT AND LOOSE TRANSITION-STATES IN UNIMOLECULAR DISSOCIATIONS

Measuring the cross-over point in breakdown diagrams for different sample temperatures provides a simple method to determine the threshold energy, E0(J), for the unimolecular dissociation of many ions. The variation of E0(J) with the angular momentum of the molecule depends strongly on the characteristics of the potential energy surface. It is shown by comparison with available data for the dissociation of ethyl chloride and some alkane ions that this method allows one to distinguish tight from loose transition states.