Femtosecond real-time probing of reactions. II. The dissociation reaction of ICN

Experimental results obtained for the dissociation reaction ICN*→I⋅⋅⋅CN‡*→I+CN using femtosecond transition-state spectroscopy (FTS) are presented. The process of the I–CN bond breaking is clocked, and the transition states of the reaction are observed in real time. From the clocking experiments, a ‘‘dissociation’’ time of 205±30 fs was measured and was related to the length scale of the potential. The transition states live for only ∼50 fs or less, and from the observed transients we deduce some characteristics of the relevant potential energy surfaces (PES). These FTS experiments are discussed in relation to both classical and quantum mechanical models of the dynamical motion, including features of the femtosecond coherence and alignment of fragments during recoil. The observations are related to the radial and angular properties of the PES.